Antioxidant activity of Ulva reticulata extract was carried out for proving its utility in free radical mediated diseases including diabetic, cardiovascular, cancer etc. The seaweed extract was screened for in vitro antioxidant activity by oxygen radical scavenging such as DPPH, total antioxidant assay, superoxide, hydroxyl radical and Nitric oxide scavenging activity at different concentrations. Throughout the study seaweed extract showed marked antioxidant activity. The antioxidant activity of the seaweed extract may be due to the phytochemicals present in it. The antioxidant activity was found to be concentration dependent and may be attributed to the presence of bioflavonoids in Ulva reticulata extract. Overall, the seaweed extract is a source of natural antioxidants which might be helpful in preventing the progress of various oxidative stress mediated diseases including aging.