Abstract: The composition, distribution and biodiversity of cyanobacteria were investigated in relation to salinities of several saltpans of Southeastern coasts of India from Vedharnyam (10 °22` N; 79 °51` E) to Mandapam (9 °17` N; 79 °7` E). Sixty one species belonging to 21 genera and six families were identified. The salinity was ranged from 48 to 185 ppt. Almost all species were found along the range from 48 to 89 ppt., while there was a relative reduction in species composition and biodiversity with salinity of 150 and 185 ppt. The most widespread cyanobacteria were Spirulina subsalsa, S. labyrinthiformis, Oscillatoria willei, O. salina, O. subbrevis, O. laete-virens, Phormidium tenue and Microcoleus chthonoplastes. Aphanothece microscopica, Arthrospira platensis, Dermocarpa leibleiniae, Oscillatoria terebriformis, Oscillatoria acuminata and Synechocystis salina were limited in their distribution to lower salinities. Nostoc sp. was the only heterocystous form recorded in the hypersaline environment.