This paper we reports the diatom assemblages collected in Lake Kusyu-ko on Rebun Island, Hokkaido, in August 2005, A total 80 taxa, belonging to 29 genera were found from this lake. The dominant taxa and subdominant taxa were Epithemia adnata (62.4%) and Rhopalodia gibba var. ventricosa (13.3%) found in the sediment.
