The antioxidant enzyme activities in the leaves of Alternanthera philoxeroides seedlings, an alien invasive species, were investigated under 2℃ and 8℃ low temperatures compared with the normal temperature 28℃. The results were as follows. As for malondialdehyde(MDA) and membrane permeability, there were only a little changes under 8℃, but they showed significant increases after 36h under 2℃. The activities of cell protective enzymes-superoxide dismutase(SOD), catalase(CAT) and peroxidase(POD) increased significantly in 12h and then decreased gradually under 2℃. Moreover, CAT activity was inhibited more severely than those of SOD and POD activity after 48h by 2℃ low temperature stress. 3 cell protective enzymes SOD, CAT and POD activity all increased significantly in 48h under 8℃, but they changed less than those under 2℃. It gave us a hint that 8℃ low temperature stress probably could not inhibit, but promote cell protective enzymes activity in 48h for leaves of A. philoxeroides seedlings. When the seedlings stressed by low temperature were subjected to normal temperature, there were little difference between the seedlings under 8℃ and the seedlings under normal temperature after 10d; however, some morphological differences of the seedlings appeared under 2℃.