To understand the algal community structure,cell abundance and dominant species,Taizi River catchment,Liaohe River basin were investigated four times,from September 2010 to September 2011.Algae,including 8 phyla,120 genera,328 species (including 21 varieties) were identified from 17 sampling sites.Bacillariophyta were the dominant algae and included 36 genera,144 species,accounting for 43.77% of the algae.Chlorophyta,with 49 genera,117 species,accounted for 35.56% of the algae.Cyanophyta,included 22 genera,38 species and accounted for 11.85% of the algae.The cell abundance of algae was higher in summer and autumn,which were 6.80×10⁷ and 3.29×10⁷ cells/L,respectively.However,it was lower in spring with 1.36×10⁷ cells/L.This study also demonstrated that the dominant species of algae in Taizi River catchment were more than five, including Oscillatoria princeps Vauch.,Hormidium flaccidum (Kütz.) Br.and Stigeoclonium subsecundum (Kütz.) Haz.ect.Species Jaccard index of the algae varied from 0.19 to 0.46.Both algal community structure and cell abundance have obvious seasonal variation in Taizi River catchment.