Moutan Cortex Radicis (MCR) is one of the most widely used Oriental medicines. In this study, we assessed the reducing effect of ethanol extract of MCR on hydrogen peroxide-induced reactive oxygen production, the main cause of cell damage or death in PC12 cells. The viability of cells treated with 1 mg/ml of MCR was significantly restored from that of oxidative-stressed PC12 cells. Measurement of intracellular reactive oxygen species (ROS) generation was determined using the H(2)DCFDA assay. MCR at 1-0.01 mg/ml concentration inhibited ROS production in oxidative-stressed cells. To identify candidate genes responsible for the anti-oxidative effects of MCR on PC12 cells, an oligonucleotide microarray analysis was performed. The result of gene expression profiles showed that 10 genes were up-regulated and 7 were down-regulated in MCR plus hydrogen peroxide treated cells compared with hydrogen peroxide treated cells. Among them, heme oxygenase (HO) and cathechol-O-methyltransferase (COMT) are related to regulation of ROS generation and the others are known to regulate cell survival and progression. Subsequently, we performed real-time RT-PCR to quantify the ROS related gene. MCR treatment increased the expression of HO by 370% and COMT by 280% at the concentration of 1 mg/ml. These findings suggest that MCR inhibits the production of ROS and cytotoxicity by oxidative-stressed PC12 cells through over-expression of HO and COMT.