Alloxan administration in male albino rats, induced diabetes by increasing blood glucose concentration and reducing hepatic glycogen content as compared to normal control group. Besides, serumlipid profile parameters such as total-cholesterol, triglyceride, low-density lipoprotein and very lowdensity lipoprotein cholesterol were also elevated, whereas, the level of high-density lipoprotein-cholesterol was reduced significantly (P<0.05) in diabetic rats. Treatment of diabetic animals with hot aquous extract of Cystoseira myrica for 30 days, significantly lowered blood glucose level, elevated hepatic glycogen content and maintained body weight and lipidprofile parameters towards near normal range. Declined activity of antioxidant enzymes and concentration of non-enzymatic antioxidants were also normalized by drug treatment, thereby reducing the oxidative damage in the tissues of diabetic animals and hence indicating the anti-diabetic and antioxidant efficacy of the extract. Biochemical observations were further substantiated with histological examination of pancreas and liver.