Octacosanol is known to enhance endurance activities, control cholesterol in body and improve the function of cardiopulmonary. Citrulline, which is main compound of watermelon, is known to improve angiectasia through stimulating production of nitric oxide. To improve endurance activity swimming test on rats was carried out using four samples such as 1$\%$ octacosanol, citrulline, the extracts of barks of watermelon and products, mixture of 1$\%$ octacosanol and the extracts of barks of watermelon (6 : 4). Biochemical assays on the liver and serum of tested rats were also performed using commercial analysis kits. In result, it was shown that swimming time of III group increased by 26$\%$ and that of V group was increased by 22$\%$ at the swimming test. As a result of biological assays on the liver and serum of tested rats it was possible to confirm stability of toxicity When compared with creatine kinase of control group (549.11$pm$39.15 U/l) citrulline (644.11 $pm$50.67 U/l) and products group (646.00$pm$46.99 U/l) were largely increased. When compared with inorganic phosphate of control group (12.01$pm$0.75 mg/이), citrulline (13.03$pm$0.94 mg/dl) and products group (12.90$pm$0.55 mg/dl) showed similar results. Also, when compared with lactic acid and glucose of control group (152.91 $pm$ 13.45, 103.00$pm$ 8.69 mg/dl), citrulline (125.53$pm$15.54, 83.75$pm$7.29 mg/dl) and products group (135.26$pm$11.50, 78.57$pm$9.79 mg/dl) were largely decreased. As these test results, it was determined that 1$\%$ octacosanol and extracts of barks of watermelon had some effect of improving endurance activity. Futhermore, it was thought that it could be used as source of functional food.