Abstract: The effects of metal ions Mo6+，Cu2+，and Zn2+ on the activities of mixed moderately thermophilic bacteria such as Leptospirillum ferriphilum and Acidithiobacillus caldus，were tested by the metal tolerance experiment. As results，the activities of mix moderately thermophilic bacteria decreased with increasing concentration of metal ions. The tolerated concentration of bacteria tested for metal ions Mo6+，Cu2+ and Zn2+ were 0.6 g/L，10 g/L and 30 g/L respectively. The toxicity order of metal ions was in Mo6+ >Cu2+>Zn2+. A. caldus presented a higher degree of resistance to metal ions than L. ferriphilum. Results in this study demonstrated that L. ferriphilum and A. caldus in co-culture had strong resistance to metal ions，especially to Mo6+，thus it can be applied to the bioleaching for molybdenum sulphide ore，molybdenum waste and molybdenum sludge.

Key words: metal ion, moderately thermophilic bacteria, Acidithiobacillus caldus, Leptospirillum ferriphilum, activity