Hamachō Park, Urban park in Nihonbashi-Hamachō, Japan

Hamachō Park is a 46,531 m² ward-run park in Nihonbashi-Hamachō, the largest in Chūō Ward, facing the Sumida River near Shin-Ōhashi. It holds a lawn plaza, a playground, a day-camp area, the Hamachō sports ground, the Chūō Ward General Sports Center with pool, golf range and archery hall, and the Seishōkō-ji temple. The Toei Shinjuku Line runs beneath it, and an underground car park of irregular shape lies under the north sports ground.

The park opened in 1929, laid out under Gotō Shinpei's Teito Reconstruction programme after the 1923 Great Kantō earthquake, together with Sumida Park and Kinshi Park. Its grounds had earlier held Edo-period lower residences of the Hitotsubashi Tokugawa, Makino, Tsugaru and Hosokawa families, and later the Hosokawa and Nagaoka viscount estate.

Inside the park stands Seishōkō-ji, a temple to Katō Kiyomasa. The Kumamoto domain lord's family enshrined it in 1861 within their residence, and it was open to public worship while the Hosokawa family still owned the land. It was later called Katō Shrine and then Hamachō Seishōkō-dō.

The grounds have public restrooms, drinking fountains, and playgrounds distributed at different locations. Proximity to public transportation makes visiting straightforward.

The Toei Shinjuku Line runs directly beneath the park, crossing it east to west; Hamachō Station lies under the grounds. During the line's construction, the park served as a base for removing soil from the shield machine and for bringing in segment blocks. The underground car park below the north sports ground has an irregular shape because the subway cuts diagonally beneath it.