Abstract: Seasonal variations of Phytoplankton dynamics were noted both quantitatively and qualitatively at Puri Sea Shore of Bay of Bengal. In total of Phytoplanktons, 45 species of Chlorophyta (53.60%), 17 species of Bacillariophyta (29.45%) and 12 species of Cyanophyta (16.75%) were identified. Phytoplanktons are producers or photosynthetic organisms as they bear photosynthetic pigments which converts solar energy into chemical sugars, consumed by consumers or heterophes. Thus they are vital to marine eco system.