Algae were diagnosed in three stations at three seasons for 2018-2019 in the Tigris River. It was diagnosed with 158 species for five main divisions (Chlorophyta, Bacillariophyta, Cyanophyta, Pyrrhophyta and Euglenophyta). Chlorophyta division represented 14 genera and 33 species with a percent of 20.88%, Bacillariophyta division was 22 genus and 84 species with a percent of 53.16%, division Cyanophyta was14 genus and 41 species with 25.94%, pyrrhophyta division was four genus and four species with 2.53%, and the Euglenophyta division was one species with 0.63%. The study also showed the essential common species for quantitative and qualitative studies within the study stations: Chlorella vulgaris, Oscillatoria lemmetica, Amphiprora alata, Nitzschia clausii and Navicula enigmatica. In conclusion, the study showed an abundance of algae densities within the study sites. Keywords: Classification, Algae, Tigris River.