A biological membrane is the frontier of the cells against the environmental reactive oxygen species (ROS) and is expected to play an important role in the antioxidant system corporately with antioxidant enzymes. The response behaviors of the antioxidant enzymes (superoxide dimutase (SOD) and catalase (CAT)) were investigated in the presence of artificial membrane, liposome, under the oxidative stress condition in order to obtain the fundamental information for the ROS scavenger system. The intracellular antioxidant enzymes, SOD and CAT, are known to make protective system against ROS. Although the SOD is known to catalyze the dismutation of ·O₂- to H₂O₂. The activity of SOD was lost thoroughly in the presence of H₂O₂ at high concentration (>5mM). The SDS-PAGE analysis showed that the SOD was fragmented into several small peptides. SOD has two -helix loops, which introduce the substrate ·O₂- to the activity center of SOD (Cu(II)). From the circular dichroism analysis of SOD in the presence of H₂O₂, the contents of α-helix in the SOD were found to decrease in corresponding with the inactivation of the SOD, suggesting that the conformation of the α-helix loops might be varied. However, the SOD was not inactivated in the presence of POPC liposomes while the contents of α-helix were decreased similarly in the case of that without liposome. Based on these results, the possibility to develop the ROS scavenger system using the SOD and CAT together with liposome was finally discussed.