In the present work, impact of UV-B radiation (280- 315nm: 0.4 W m-2) on growth, photosynthetic pigments, protein, ascorbate, proline and lipid peroxidation have been studied in two cyanobacteria Nostoc muscorum and Synechocystis PCC 6803. UV-B radiation (2 to 6 hrs) leads to 55% inhibition of growth in Synechocystis PCC 6803 as comparison to control where as in Nostoc muscorum growth reduces up to 45%. This UV-B treatment also significantly decreased the contents of chlorophyll, carotenoids and phycocyanin. Photosynthetic pigments decreased with increasing doses of UV-B (2 to 6 hrs) radiation. However, the inhibitory effect in Synechocystis PCC 6803 was more pronounced than in Nostoc muscorum. With increasing UV-B exposure period, production of ascorbate (19- 45%), proline (12-29%) and lipid peroxidation was significantly higher in Synechocystis PCC 6803 as compared to control sample. It was observed that lipid peroxidation enhanced 33 % than control sample of Synechocystis PCC 6803. Our result shows that photosynthetic apparatus is the main target of UV-B radiation causing degradation of photosynthetic pigments. This study concluded that Synechocystis PCC 6803 was the susceptible organism for survival in stress condition than Nostoc muscorum.