10.22376/ijpbs.2019.10.1.p1-12 Volume 2 Issue 1 2011 (January - March) The seaweeds are a promising source of natural products. In the present study, preliminary phytochemical analysis concluded that due to the presence of extra phytochemical in Ulva fasciata when compared to the Chaetomorpha, this alga is a beneficial one for its biological activity. In the DPPH scavenging assay, both the seaweed extracts showed high antioxidant activity. The Ulva fasciata samples have more effective antioxidant activity when compared to the Chaetomorpha antennina. And the percentage of scavenging was found to be about 83.95% for U. fasciata and 63.77% for C. antennina sample. The rapid TLC assay is considered as the rapid test to evaluate the antioxidant activity of natural compounds. The compounds showing the bands at hRf = greaterThan 10, 25 and 94 of both the seaweed extracts and hRf = 52 in Ulva sp alone were proved to be having antioxidant activity. The results of antimicrobial activity by the well diffusion assay also clearly expressed that Ulva fasciata has high concentration of active principles when compared to the Chaetomorpha antennina.  lessThan br / greaterThan PREMALATHA.M.,DHASARATHAN. P,P. THERIAPPAN 288-293