Comparison of protective effects between cultured Cordyceps militaris and natural Cordyceps sinensis on hepatotoxicity was investigated. Water extracts of C. militaris (CME) and water extracts of C. sinensis (CSE) protected the HepG2 cells against t-butyl hydroperoxide (t-BHP) induced oxidative injury. No significant differences were found between CME and CSE at 500 μg/mL in ROS generation, GSH content, TBARS formation, Bcl-2/Bax ratio in t-BHP-induced HepG2 cells. The inhibitory effect of CME at 500 μg/mL on caspase 3 activity in t-BHP-induced HepG2 cells was superior to CSE (500 μg/mL). However, protective effect of CME on decreasing the mitochondria membrane potential in t-BHP-induced HepG2 cells was inferior to CSE. The hepatoprotective actions of CME and CSE in vitro may be related to maintenance of the normal redox status of cells. Taken together, our results suggest that CME could be a potentially useful source in substitution for CSE for preventing and treating hepatotoxicity.