Cirsii Japonici Herba (CJH) extract has been used for hundreds of years in Asian countries as a treatment for pollutant, radiation, and alcohol-induced liver damage. The reducing effect of CJH on hydrogen peroxide-induced reactive oxygen species (ROS) production, the main cause of cell damage or death, was evaluated using the HepG2 cell line. Cell survival was determined using MTS assay. The viability of cells treated with CJH was not significantly different from oxidative-stressed HepG2 cells. A dose-dependent inhibitory effect by CJH on ROS production was shown in oxidative-stressed cells using the $H_{2}DCFDA$ assay. To identify candidate genes responsible for the anti-oxidative effects of CJH on HepG2 cells, an oligonucleotide microarray analysis was performed. The expressions of five genes were decreased, whereas nineteen genes were up-regulated in CJH plus hydrogen peroxide treated cells, compared to only hydrogen peroxide treated cells. Among them, the expression of 5 genes was decreased in hydrogen peroxide treatment when compared to control. These genes are known to regulate cell survival and progression. On the other hand, it was shown that its main compounds were not a sylimarin or its analogs. The list of differentially expressed genes may provide further insight on the action and mechanism behind the anti-oxidative effects of Cirsii Japonici Herba.