Hibiscus protocatechuic acid (PCA), a simple phenolic compound isolated from Hibiscus sabdariffa L., was studied for its protective effects against oxidative damage induced by tert-butylhydroperoxide (t-BHP) in a primary culture of rat hepatocytes. It had been reported that exposure of isolated hepatocytes to t-BHP results in leakage of lactate dehydrogenase (LDH) and alanine transaminase (ALT), peroxidation of cellular lipids, and depolarization of mitochondria. The present investigations showed that PCA at concentrations of 0.05 mg/ml and 0.10 mg/ml significantly decreased the leakage of LDH (P < 0.01) and ALT (P < 0.05 and P < 0.01) and the formation of malondialdehyde (MDA; P < 0.05 and P < 0.01) induced by 30-min treatment with t-BHP (1.5 mM) in primary cultured rat hepatocytes. PCA also attenuated t-BHP (0.10 mM) induced mitochondrial depolarization as determined by a retention test of rhodamine 123 and DNA repair synthesis as evidenced by unscheduled DNA synthesis (UDS). In addition, PCA exhibited an effective ability to quench 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH). In conclusion, PCA demonstrated protective effects against cytotoxicity and genotoxicity of hepatocytes induced by t-BHP. One of mechanisms of PCA's protective effect may be associated with its property of scavenging free radicals.