Zhoushan Island island of the namesake archipelago Zhoushan Islands, administered by Zhoushan City, Zhejiang Province, the People's Republic of China. Its name means "Boat Mountain", in reference to its shape. It is the province's largest island, and third largest in mainland China (after Hainan and Chongming Islands). The island is the district seats of both Dinghai and Putuo.
It lies northwest to southeast, and has a circumference of 170.16 km (105.73 mi), with a maximum length of 44 km (27 mi), and a maximum width of 18 km (11 mi). Its area is 502.65 km2 (including tidal zone). At its closest point, it is 9.1 kilometres from the Chinese mainland. The tallest point is 503.6 metres.
The island has varied range of landscape, with hill and dale, as well as watered with numerous small streams, of which the most considerable is the Dongjiang (East River), passing into the harbour of Dinghai. There are several hundred ports around the islands, separated into three areas: Dinghai Port Zone, Shen-jia-men Port Zone, and Laotangshan Port Zone. The tourism regions include the regions of Shen-jia-men and Dinghai.