Guichen Bay, is a bay located on the south-east coast of the Australian state of South Australia about 115 kilometres northwest of the regional city of Mount Gambier and about 270 kilometres south-southeast of the state capital of Adelaide. It was named in 1802 by the Baudin expedition of 1800-03 after Luc Urbain de Bouëxic, comte de Guichen. The town of Robe is located at the southern end of the bay.

The Baudin expedition of 1800 to 1803 was a French expedition to map the coast of New Holland. Nicolas Baudin was selected as leader in October 1800. The expedition started with two ships, Géographe, captained by Baudin, and Naturaliste captained by Jacques Hamelin, and was accompanied by nine zoologists and botanists, including Jean-Baptiste Leschenault de la Tour, François Péron and Charles-Alexandre Lesueur as well as the geographer Pierre Faure.