To prove the relationship between the fluctuation in serum beta-glucuronidase level and hepatotoxicity, an inhibitor of beta-glucuronidase from G. lucidum was isolated and its hepatoprotective activity was investigated. The ether fraction of G. lucidum, which had potent beta-glucuronidase-inhibitory activity, protected against CCl4-induced liver injury. From this ether fraction, ganoderenic acid A, was isolated as the potent inhibitor of beta-glucuronidase. It had a potent hepatoprotective effect against CCl4-induced liver injury. These results suggest that the beta-glucuronidase seems to be closely related to liver injury, which could be prevented by beta-glucuronidase inhibitors.