Several Plant products have been found to be a part of phytomedicines since time immemorial. These plant products can be derived from barks, leaves, flowers, roots, fruits, and seeds. It has been found that the light radiation affects the antimicrobial activity of herbal products. The present study was aimed to investigate the phytochemical screening and antimicrobial activities of Calotropis gigantea leaf extracts. In addition to these studies we also check the effect of UV light radiation on the anti microbial activity of leaf extract. Phytochemical screening revealed the presence of various active phytochemicals in the extracts of aerial part of Calotropis gigantea. Ethanol, chloroform and hexane extract of leaves were tested against Clostridium botulinum, Proteus vulgaris, Escherichia coli and Arthrographis cuboid, Aspergillus fumigatus, Aspergillus niger by the agar disc diffusion method. The antimicrobial activity of the extracts generally reduces significantly after exposure to the UV radiations.