The effects of various fractions from the whole plant of Pelvetia siliquosa Tseng et Chang (Fucaceae) on the $CCl_4$-induced hepatotoxicity as well as on streptozotocin (STZ)-induced diabetes in rats were investigated. The ether fraction exhibited a potent rat lens aldose reductase (RLAR) inhibition in vitro and showed a significant inhibition of not only serum glucose concentrations but also sorbitol accumulations in the lens, red blood cells and sciatic nerves in the STZ-induced diabetic rats. When administered orally in Sprague-Dawley rats, $H_{2}O$ fraction was found to cause a significant inhibition of the rise in the serum transaminase activities in $CCl_4$-intoxicated rats. These results suggested that this plant might possess constituents with hepatoprotective, anti-diabetic effects and those effects on diabetic complications.