Natural products from the marine source have drawn attention of researchers worldwide over the last few decades. Preliminary phytochemical screening and in-vitro antioxidant potential were analyzed for the red alga Codium adhaerens collected from the Pudumadam region, Rameswaram. Phytochemical analysis revealed the presence of major phytoconstituents phenolics, flavonoids, alkaloids, proteins, tannins and terpenoids. Ethyl acetate extract were tested for total phenolic and flavonoid content, total antioxidant activity, reducing power assay, scavenging activity on DPPH, Superoxide anion, nitric oxide and hydrogen peroxide radicals. The total phenolic and flavonoid content were found to be 53.11 ± 0.29 mg/g Gallic acid equivalents and 52.45 ± 0.37 mg/g Quercetin equivalents. The total antioxidant activity were found to be (74.61 ± 1.55)% at 1000μg. Ethyl acetate extracts exhibited maximum scavenging activity against free radical DPPH (72.92 ± 0.23)%, Superoxide anion (59.41 ± 1.58)%, Nitricoxide (52.41 ± 1.40)% and hydrogen peroxide radical (49.17 ± 0.83)% Hence, it can be concluded, red alga Codium adhaerens has bioactive compounds with remarkable antioxidant activity.