A list of diatoms found in the region of Cananéia is given in this paper. A description is given of the diatoms recorded for the first time in Brazilian waters (Eunotia major (W. Sm.) Rabh., Eunotia praerupta var. bidens Grun., Eunotia sudetica O. Muller, Nitzschia ançrularis W. Sm., Nitzschia fluminensis Grun., Nitzschia macilenta Greg., Nitzschia sigma (Kütz.) W. Sm. var. intercedens Grun., Surirella guatimalensis Ehr., Surirella kittoni A. S., Synedra acus Kütz. var. angustissima Grun., Triceratium uncinatum A. S., Tropidoneis seriata Cleve) as well of those of some interest due to their geographic distribution. The species studied are cosmopolitan and tropical and only one is a characteristic species of cold water (Chaetoceros tortissimus Gran.), the presence of which could not be explained based on the physical data obtained (temperature and salinity). The basic factor that influences the nature and horizontal distribution of the phytoplankton was found to be salinity.
