Abstract: A pot experiment in simulated field ecological environment was carried out to study effect of slow/controlled release fertilizers on soil biological activity of urease and nitrate reduetase,microbial biomass carbon and nitrogen in the soil at the maize seedling stage.Results show that soil urease activity was significantly inhibited at the maize seedling stage by nBPT-coated urea(nBPT is a kind of urease inhibitor)and starch-acetate-nBPTcoated urea down to 49.25 and 48.13(μg·g~(-1)·d~(-1)),respectively,whereas nitrate reduetase activity was enhanced in all fertilizer treatments up to 0.76～1.03 μg·g^-1·d^-1,showing no big difference between each other.The urease inhibitor nBPT did not have any inhibiting effect on soil nitrate reduetase activity.The effects of slow/controlled release fertilizers on soil microbial biomass carbon and nitrogen were more or less the same.Soil microbial biomass was the highest in the treatment of nBPT-coated urea with microbial biomass carbon and nitrogen being 248.19 and 56.53 mg·kg^-1,respectively,and the lowest in the treatment of methyl-methacrylate-nBPT-coated urea,with microbial biomass carbon and nitrogen being 104.80 and 23.94 mg·kg^-1,respectively.The characteristics of the change in soil biological activity at the maize seedling stage show that the combination of methyl methacrylate and urea inhibitor nBPT is the most effective coating in controlling release of nitrogen from the fertilizer.