The effects of lanthanum on some redox system(PMRS) properties of the plasma membrane(PM) vesicles from Casuarina equisetifolia seedlings under artificial acid rain(pH 4.5)stress were studied. The results show that there are NADH oxidase and EDTA-Fe3+ reductase, and nitrate reductase in the seedling PM, and they have different responses to soaking seeds for 8 h in a series of LaCl3 solution. The NADH oxidase activities and the Nitrate reductase activities can be stimulated when La3+ concentrations is in the range of 50～200 mg*L-1, but their activities are inhibited or fluctuate by the higher La3+ concentrations. The EDTA-Fe3+ reductase activities can be stimulated by La3+ concentrations in the range of 50～400 mg*L-1. The research also revealed that La3+ reduces the relative permeability of membranes and have the function in protecting membranes under acid rain stress by the way of inhibiting the leakage of electrolyte.