Cadmium is one of the widespread trace pollutants in soil and water with a long biological half-life, causing heavy toxicity to humans, animals and edible fungi. Pleurotus ostreatus, a popular edible fungus, which is widely cultured in China, could accumulate and turn over Cd that enters into human body through the chain of food. Although there are accumulating reports concerning the toxicity of Cd in plants and animals, very little is known about that in edible fungi. To understand how P.ostreatus accumulates and detoxifies Cd at biochemical level, we used P.ostreatus 17 strain to study the effects of Cd on mycelial growth and isozymes pattern of P.ostreatus. After 7 days P ostreatus was cultured in PDA medium, containing various concentration of Cd, mycelia were harvested, homogenized and then the supernatants from the homogenate were used for enzyme analysis using PAGE and isozyme staining. To investigate the role of mycelial metallothionein of P.ostreatus involved in turning over of Cd, metallothionein content was determined by a Cd-saturation method. The results showed that Cd at 50 μmol/L could inhibit the growth of mycelia by 55.6%, and a lethal dose of metal for mycelia was 2000 μmol/L.The analysis of native PAGE enzyme activity staining revealed that exogenously applied Cd not only modulated the activities of peroxidase (POD E.C.1.11.1.7), superoxide dismutase（SOD E.C1.1.5.1.1）, esterase (EST E.C.3.2.1.1) and lactate dehydrogenase（LDH E.C.1.1.1.27), but also the expression patterns of these isozymes. Total POD activity was drastically enhanced in mycelia treated with cadmium at 50 and 100 μmol/L, whereas additional isozymes bands were induced while a band with the highest molecular weight was suppressed. Two bands of LDH isozymes were observed in mycelia of P. ostreatus without Cd treatment, and the LDH pattern was not affected by Cd below 50 μmol/L. However, the activity of LDH was completely inhibited in mycelia treated with 100 μmol/L Cd. Cadmium at 50 and 100 μmol/L caused significant changes in the total activity of SOD and induction of two new isozyme bands. Treatment with 10～100 μmol/L Cd resulted in an increase of EST activity, suggesting a role of EST in detoxification of Cd. Moreover, metallothionein content was markedly increased in mycelia in the presence of Cd at 10 and 20 μmol/L Cd, however, the induction of metallothionein by Cd at 100 μmol/L attenuated remarkably, suggesting that metallothionein plays an important role in complexing with Cd ion inside the cell at low concentration Cd stress.