Abstract: Fe 2+-Mn2+oxidizing sheathed bacteria is a group of bacteria with ability to oxidize Fe2+ and Mn2+.In practice they were used to treat wastewater.Previous researches indicated that the functional component for Fe 2+-Mn2+ oxidation in the bacterium is Fe2+oxidase.Because of the low content and easy inactivation,Fe2+oxidase is difficult to be purified.This resulted the less information about the properties of the enzyme.A strain of Fe2+ oxidizing sheathed bacteria Sphaerotilus natans FC9901 we separated previous was used as material for Fe2+oxidase investigation in this paper.Serial culture media were employed to culture the bacterium so as to explore the optimum conditions for enzyme productivity.The modified TMPD method was used to measure the enzymatic activity.After partially purification by ammonia sulfate precipitation and dialysis,the enzymatic properties were analyzed.The results were as follows:the optimum culture medium for enzyme production:10g citrate,1.2g NaNO3,0.5gMgSO4, 0.5g K2HPO4·7H2O,0.005g CaCl2,and 0.0005g ZnSO4·7H2O per litre.The optimum cultural condition for enzyme production in shaking flask:temperature 30℃,initial pH 7.0,medium volume 50ml/150ml flask, inoculum concentration 2%,shaking speed 150r/min,culture period 72 hours.The optimum temperature and pH for enzyme production during the culture:30℃and 7.5,respectively.The enzyme was very sensitive to temperature.At the optimum temperature(30℃),the purified enzyme could be stored for 150min.Inactivation of the enzyme was very quick with the increase of temperature.When temperature was as high as 50℃,the enzymatic activity would completely lost within 5min.The enzyme was relative stable in the range of pH 7.0～8.0.basic solution was more harmful to enzymatic activity than acidic.The oxidizing activity of the enzyme could be activated by Ca2+,Mg2+ and Zn2+,whereas Cu2+,Hg2+ and Al3+ could inhibit the enzymatic activity.No effect of Fe 2+,K+ and Na+ on enzymatic activity was observed.