The purpose of this study was to investigate the anti-oxidant effect of Cynomorium songaricum. The extract of Cynomorii Herba was studied for diphenyl-picryl-hydrazyl (DPPH) radical scavenging activity, HepG2 cell viability and $H_2O_2$-induced cytotoxicity by a modified MTT assay. DPPH radical scavenging activity was measured after 30 minutes. The extract was tested by 1. 5, 10, 50, 100 and 500 ${mu}g/ml$ concentrations. HepG2 cell viability by a modified MTT assay was measured in the concentrations of 10, 50, 100, 250, 500 ug/ml for 24 h. The results showed that the extract scavenged DPPH radical up to 52.2% with 50 ug/ml concentration. The extract did not reduced the cell viability and $H_2O_2-induced$ cytotoxicity (69.4%) was blocked by the extract in the concentrations of 50, 100, 250 and 500 ${mu}g/ml$. In conclusion, the extract of Cynomorii Herba has potent antioxidant activity.