Abstract: Common bean [Phaseolus vulgaris L.] plants were cultured in solution with Mg deficient (0 mmol/L) and nirmal Mg supply [1. 2mmol/L]. Plants under Mg deficiency showed intervenial chlorosis, necrosis in primary leaves and first trifoliate leaves. Normal Mg supply increased plants dry matter weight and concentration of Mg in leaves, stems, and roots. There was little difference of concentration of chlorophyll between those leaves without yellow and chlorosls under Mg deficiency and normal leaves with Mg sufficiency, but concentration of chlorophyll in yellowish leaves from Mg deficiency was lower. Hill reaction values of intact chloroplasts in Mg deficient leaves were similar to those in Mg sufficient lesves. Mg deficiency caused the increase of relative electric conductance in extracting solution of lesves and roots. Concentration of malondialdehyde also remained pronounced levels in leaves. Comparing to Mg sufficient leaves, the activies of superoxide dismutase (SOD, EC 1. 15. 11), ascorbate peroxidase [AsA-POD, EC 1. 11. 17], guaiacol peroxidase (EC1.11. 17) and catalase(CAT. EC L 11. 16) were significantly enhanced inthe leaves by Mg deficiency. It seemed that Mg deficiency affected plasma membrane permeability, membrane llpld peroxldatl0n and endogenous oxygen radicals scavenglng enzymes Systems in bean seedlings.