Dinghai (定海区) is a Chinese district of Zhoushan City made of 128 islands. It is based on the larger northwestern half of Zhoushan Island, where it borders Putuo in the east. The district boundary meets that of Daishan County entirely on sea to the north. Its southwestern boundary intersects those of Ningpo City entirely on sea.
The island is the district seats of both Dinghai and Putuo.
The island is beautifully diversified with hill and dale, and well watered with numerous small streams, of which the most considerable is the Tungkiang, faffing into the harbour of Dinghai.
There are several hundreds of ports around the islands, separated into three areas: Dinghai Port Zone, Chengjiamen Port Zone (沉家门港区), and Laotangshan Port Zone (老塘山港区).