Portsea is a suburb in Melbourne, Victoria, Australia. Its Local Government Area is the Shire of Mornington Peninsula.

Portsea is located near the end of the Mornington Peninsula, and is considered by many to be the hub of Melbourne's recreational scuba diving activities. No less than four scuba related shops operate from in its otherwise modest main street. Dive boats travel to sites both inside Port Phillip and outside the heads.

The Portsea Pier is the home to the spectacular leafy sea dragon, as well as many other fish species, including numerous pufferfish. Boating traffic is frequent, and divers should be careful to avoid main boating routes.

Harold Holt, a former Prime Minister of Australia, disappeared while swimming near Portsea on 17 December 1967 and was officially presumed dead two days later.