As part of a species richness survey and ecological investigation of intertidal epilithic cyanobacteria, samples were collected during winter (November 1998-March 1999) and summer (July-September 1999) from various rocky shores around Hong Kong. Morphological and ecological descriptions are provided for 15 species belonging to the genus Oscillatoria , namely Oscillatoria cf. annae , O. bonnemaisonii , O. cf. borneti , O. brevis , O. chalybea , O. cf. curviceps , O. cf. irrigua , O . cf. limosa , O. margaritifera , O. cf. obtusa , O. cf. ornata , O. cf. princeps , O. cf. proboscidea , O. cf. salina and O. sancta , all of which are new records for Hong Kong. Of these, eight species ( O. cf. annae , O. cf. borneti , O. cf. curviceps , O. cf. irrigua , O. cf. obtusa , O. cf. ornata , O. cf. proboscidea and O. cf. salina ) are reported for the first time as marine epiliths. Most of the species were restricted to the mid- and lower eulittoral shore and were found in the winter months.