Effects of the EtOH extract from Pelvetia siliquosa on $CCl_4$-induced hepatotoxicity as well as streptozotocin-induced diabetes in rats were investigated. The EtOH extract was found to cause an inhibition of the rise in the transaminase activities in $CCl_4$-intoxicated rats. Also, the EtOH extract exhibited a rat lens aldose reductase inhibition in vitro and showed an inhibition of not only glucose concentrations but also sorbitol accumulations in the lenses, red blood cells and sciatic nerves in the STZ-induced diabetic rats in vivo. These results suggested that this plant might possess hepatoprotective and anti-diabetic activities.