Marine cyanobacteria were isolated from water samples of the three mangrove site in Kurusadai island, south east coast of India. Totally 12 species of cyanobacteria were recorded in which one species was heterocystous and 11 were non- heterocystous, belonging to 5 families. The species such as Oscillatoria tenuis, Oscillatoria cortiana, Oscillatoria salina and Lyngbya majuscula were identified. Among the sites, mangrove isolates of oscillatoriaceae alone contributed maximum number of cyanobacterial species (5) and minimum (1) by Nostocaceae and Synechococcaceae. In order to study the effect of physico chemical parameters on cyanobacterial abundance correlation study was done between these two factors. Salinity, temperature and pH exhibited positive correlation whereas nutrients such as nitrate, nitrite, phosphate and silicate showed negative correlation with cyanobacterial abundance.