The present study indicated that the Increase in UV-B exposure ( 312.67 nm, 2.5 Wm -2 ) to Spirulina fusiformis, a highly protein-rich (60-71%) helically coiled, unicellular, polymorphous cyanobacterium not only bleached phycocyanin (PC) but also decreased its content Absorption spectra of UV-B treated culture showed significant decline in the absorbance at the peak 620nm indicating the presence of PC. The absorbance decreased by increasing UV-B exposure. One hour simultaneous UV-B+PAR (Photosynthetic Active Radiation) exposure protected 33 percent damage of phycocyanin.