Phytoplankton in Coron Bay of the Calamianes Islands, Palawan were investigated from 27-29 May2004. Samples were collected from 33 stations by filtering five 10 L buckets of surface water througha net with a 20mm mesh bag. The phytoplankton consisted of four major groups. Diatoms, showed thehighest mean density of 1432.9indivL-1. Silicoflagellates comprised the next most abundant group witha mean density of 132.3 indivL-1. Dinoflagellates followed with a mean density of 94.8 indivL-1, while thecyanobacteria (blue-green algae) had a mean density of 19.4 indivL-1. The top three diatoms wereChaetoceros, Bacteriastrum and Coscinodiscus. The genus Peridinium was the most abundantdinoflagellate, while Tintinnopsis dominated the silicoflagellates. Among the cyanophytes, Trichodesmiumshowed the highest density. High phytoplankton concentrations were observed in the vicinity of a pearlfarm and in areas adjacent to mangrove forests. Overall abundance and diversity in the study area arehigher than in other similarly reef-dominated areas in the country. This may be attributed to factors onboth large and local scales.