There is an increasing demand for natural antioxidant molecules in order to replace the synthetic additives in the food industry. Therefore, Ulva rigida C. Agardh was analyzed to determine its bioactive components, including the total phenolic content, antioxidant capacity (lipid and water-soluble), vitamins (A, E, and C), protein, carbohydrate, and pigments. As a result, Ulva rigida showed a high total phenolic, vitamin E, and total carotene content. Hence, U. rigida could be considered as a plant possessing natural antioxidant molecules and might be useful for the food industry. U. rigida can also be used for curing diseases arising from oxidative deterioration.