The species composition, abundance and biomass of epiphyton algal communities on vegetative Phragmites australis stems were studied in two sites of mesoeutrophic Lake Gulbinas in May-October 2002. The highest species diversity, abundance and biomass were observed in June and August-September and the lowest in July. Diatoms formed up to 97.1% of total biomass in June and decreased by 44.3% in August-September. The dominants were typically epiphytic species from the genera Achnanthidium and Cymbella. Green algae comprised mainly Coleochaeate scutata, Chaetosphaeridium globosum, and species from the genera Oedogonium and Cosmarium reached the biomass maximum in August (up to 33.7%). Cyanobacteria cf. Cyanobium parvum, Geitleribactron periphyticum were prevailing at the end of P. australis vegetation. The seasonal and spatial development patterns of epiphyton algae on P. australis varied in the lake sites.