Macclesfield Bank is an elongated sunken atoll of underwater reefs and shoals in the South China Sea. It lies east of the Paracel Islands, southwest of Pratas Island and north of the Spratly Islands. It is about 130 km (81 mi) long from southwest to northeast, and about 70 km (43 mi) wide at its broadest part. With an ocean area of 6,448 km2 (2,490 sq mi) it is one of the largest atolls of the world. The Macclesfield Bank is part of what China calls the Zhongsha Islands, which includes a number of geographically separate submarine features, and also refers to a county-level administrative division.

An atoll is a ring-shaped island, including a coral rim that encircles a lagoon. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical parts of the oceans and seas where corals can develop. Most of the approximately 440 atolls in the world are in the Pacific Ocean.