Dynamic changes in activities of superoxide dismutase（SOD）, peroxidase（POD）, catalase（CAT）, polyphenoloxidase（PPO）, pectinase and cellulase of the virus-free potato seedlings and plantlets cultured in the optimal condition were measured and analyzed during different growth period in this study. The results showed that the virus-free and the optimal cultured seedlings displayed the same change trends, the activities of SOD, POD, PPO, CAT increased significantly and the activities of pectinase and cellulose decreased compared with the control. These changes could increase resistance of the potato seedlings and provide basis for their high-yield.