A theme park is planned for the former Kamiseya Communication Facility district, the site that hosts GREEN×EXPO 2027 (the Yokohama flower expo). The developers are eleven companies led by Mitsubishi Estate, which the City of Yokohama selected on 14 September 2023 as the business operator for the district’s Tourism and Vibrancy District. The proposal’s name is KAMISEYA PARK (tentative name).
The opening date has moved. The 2023 proposal targeted “around 2031,” but the planning-stage environmental scoping document Mitsubishi Estate and its partners submitted to the city on 25 March 2026 instead targets “the early 2030s.” Both the name and the timing remain provisional.
What has been decided, and by which document
| Item | Detail | Source |
|---|---|---|
| Operator | Mitsubishi Estate (lead), plus ten more companies named in the scoping document, for eleven in total | 2023 decision; 2026 scoping document |
| Name | KAMISEYA PARK (tentative name). The scoping document’s project name is “(Tentative Name) Former Kamiseya Communication Facility Tourism and Vibrancy District Development Project” | 2023 proposal; 2026 scoping document |
| Location | Tourism and Vibrancy District, spanning Kamikawai-cho (Asahi Ward) and Seya-cho (Seya Ward) | Scoping document |
| Area | Project area about 70.65 hectares; proposal site about 706,500 square metres, including a roughly 514,000-square-metre theme park zone | Proposal and scoping document |
| Visitors | About 12 million a year at opening, rising in stages toward more than 15 million | Proposal and scoping document |
| Opening | “Around 2031” moved to “the early 2030s” | 2023 proposal, then 2026 scoping document |
| Construction start | In or after 2028 | Scoping document |
| Parking | About 4,500 cars, about 450 bicycles | Proposal and scoping document |
Which part becomes the theme park, and which part stays a park
The former Kamiseya Communication Facility is a roughly 242-hectare site the US military requisitioned and returned in full on 30 June 2015. For the roughly 70 years in between, land use was restricted, though landowners largely kept farming it. In March 2020 the city drew up a basic land use plan dividing the district into four areas: Agricultural Promotion, Tourism and Vibrancy, Logistics, and Disaster Prevention and Park.
The theme park is planned for the Tourism and Vibrancy District, with a project area of about 70.65 hectares split into four zones: theme park (about 514,000 square metres), station-front (70,000), park-adjacent (65,500), and one west of the Kanjo 4 ring road (57,000), totalling about 706,500 square metres. The theme park itself sits on about 51 hectares. The scoping document notes the project area is still under discussion with the city and may change.
The Expo venue itself will keep developing afterward as the “(Tentative Name) Former Kamiseya Communication Facility Park,” across Seya-cho and Kamikawai-cho, covering about 650,000 square metres. The city calls this park, built around GREEN×EXPO 2027’s ideas and doubling as a wide-area disaster response base, a “new park” themed on “environment” and “disaster prevention.” On the theme park side, the proposal calls its park-adjacent zone the “GREEN×EXPO 2027 former venue site,” and plans nature-themed commercial facilities there around “agriculture and food” and “well-being.”
Mitsubishi Estate and ten other companies, and where the process stands
The operator was chosen through an open call. On 24 February 2023 the city sought a developer for the Tourism and Vibrancy District, aiming for “a complex visitor facility centred on a theme park,” and received a single proposal. A review committee reported back on 4 September, and the city selected Mitsubishi Estate as the business operator on 14 September.
The scoping document lists all eleven: Mitsubishi Estate (lead), Sotetsu Holdings, Tokyu Fudosan, Tokyu, Sumitomo Corporation, Takasago Thermal Engineering, Kyushu Electric Power, Kraftia, Dai Nippon Printing, Mitsubishi Warehouse & Transportation, and Fuyo General Lease. The project type is a “new Category 2 specified structure (amusement park).”
The process is at its first stage under Yokohama’s environmental impact assessment ordinance: the scoping document was submitted on 25 March 2026, and the mayor’s opinion was dated 27 May. The next step, a method statement, remains undated.
Transport from Seya Station: a busway and articulated buses, still a plan
A rail link to the district has, for now, been dropped. The city’s 2020 scoping document for the “(Tentative Name) Kamiseya Line Urban Rapid Transit Project” was formally discontinued, with a notice accepted on 27 March 2024 citing that the revised project no longer fell under either Category 1 or Category 2 of the assessment ordinance.
In its place, the city presented a busway between Seya and Kamiseya to its Building, Urban Development and Roads Committee on 13 February 2024: an underground “(Tentative Name) Seya Terminal” near Seya Station, connected by shielded tunnel to a surface “(Tentative Name) Kamiseya Terminal,” with up to three articulated buses running in a platoon and self-driving as a future goal. The city would build the infrastructure and a private operator would run the buses; the total cost is currently put at about 46.6 billion yen, targeted for the early 2030s, with the route still undecided.
The same material also describes an interchange under study, connecting the district directly to the Tomei Expressway, at an estimated cost of about 36 billion yen and also targeted for the early 2030s. Both remain at the “aiming for” or “under study” stage. How to reach the venue during the Expo itself is covered in our guide to getting to the GREEN×EXPO 2027 venue.
Construction around the venue, and what stays in the park
According to material the 2027 International Horticultural Expo Association presented at a construction briefing in May 2025, work was under way at that time around the venue on grade-separating the Meguro Koban-mae intersection on the Kanjo 4 ring road (targeted for 2026), widening Hachioji Kaido to four lanes, and tunnelling the Seyachi-nai line under the Sotetsu Main Line.
Some of what is visible during the Expo stays in the park afterward. The same material describes planting about 40 varieties and more than 600 cherry trees, meant to become a flowering, green spot local residents can keep enjoying once the Expo closes. Two single-storey park centre buildings (about 3,900 and 2,500 square metres) will serve as exhibition facilities during the Expo, then become environmental education and activity bases once the park opens.
The park’s own planning is still ahead: on 26 June 2026 the city opened a call for proposals for a “study commission for trial initiatives toward a new park plan,” with results still to be posted. Park development pauses during the Expo and resumes once it closes.
What is still undecided
The official name, opening date, ticket prices, and individual attractions appear in neither the city’s published proposal summary nor the 2026 scoping document. This remains unconfirmed. The proposal goes only as far as dividing the theme park zone into areas such as “an area gathering cutting-edge entertainment,” “an area for all ages,” and “a thrilling area,” with adaptable attractions that change through swappable video, and a note that the contents may change.