Fifty-nine species of marine benthic algae are reported for the first time from the coral reefs of isolated Swains Island, American Samoa, based on collections made during February 2002, 2004, 2006, and March 2008 under the auspices of the U.S. National Oceanic and Atmospheric Administration. The collections include 4 species of blue-green algae (cyanobacteria), 38 species of red algae, 3 species of brown algae and 14 species of green algae. Based on their frequency of occurrence at different stations during the 4 cruises, Rhipilia geppiorum and Microdictyon umbilicatum were considered the most widely distributed species during the months of February and March. Twenty-eight species represent new records for the Samoan Archipelago (American Samoa and Samoa).