Abstract: Seeds of pinns massoniana Lamb.(masson pine) from Guangxi were sown in Nanjing on April 25, 1992. The seedlings were treated with 25 and 50 mg. L-1 Paclobutrazol(PP_(333)) on October 19, during the winter time. It was shown that the electrolytic leakage of PP_(333) treated seedling leaves was decreased, the activity of superoxide dismutase(SOD) and the content of water-soluble sugar were increased. Moreover, in early spring, the activity of lAAoxidase in PP_(333) treated leaves was promoted obviously. PP_(333)(25. 50 mg. L-1) could retard the height of seedlings in the field esperiment. The fresh and dry weight of treated seedlings were superior to the control and the effects of 50 mg. L-1 were much stronger than that of 25 mg. L-1. These results suggest that 50 mg. L-1 PP_(333) can enhance the resistance of masson pine seedlings under low temperatures.