Gossaigaon is a subdivisional area of Kokrajhar district which is escaped attention of algal diversity by botanical researchers. The present studies was carried out on the diversity of family Nostocaceae, (cyanophyceae or blue green algae) during June 2017 to July 2018 (for one year) and a total 33 species were identified. However, it has attempt to explore the algal biodiversity systematically taking consideration on morphological characters. Among the identified species, Anabaena carried highest number (14) followed by Nostoc (8), Cylindrospermum (6), and Anabaenopsis, Wollea, Pseudanabaena and Aulosira represent by single species. Cyanophyceaen flora are sensitive to nutrient enrichment. It was found that the seasonal variation is a special character among these algae. Anabaena azollae is common and present in any kind of habitat water.