The effects of the MeOH and water extracts from the marine algae Pelvetia siliquosa were evaluated on hyperlipidemic rats induced by cholesterol rich diet or poloxamer-407. The MeOH and water extracts, when administered orally for 3 consecutive days in hyperlipidemic rats induced by poloxamer-407 (1 ml of 30%), were found to cause a significant decrease in plasma cholesterol and triglyceride concentrations. Both extracts also showed a significant inhibition of serum total cholesterol and triglyceride level in rats treated with cholesterol rich diet. HDL-cholesterol, however, was increased significantly.