Abstract: A pot experiment was carried out to research effects of IFC,a fertilizer synergist,on pak choi.Results show that compared with application of carbon-ammonium fertilization only,the addition of IFC improved the growth of Brassica campestris ssp.Chinensis by increasing fresh yield by 8.97%(P<0.01),dry weight by 3.45%(P<0.05),and nitrogen accumulation by 8.70%(P<0.01),and decreasing NO^- ₃-N content by 30.10%(P<0.01),but did not have much effect on nitrogen content.The effect of IFC is much better than dicyandiamide(DCD),a commonly used N fertilizer synergist.Application of IFC at a proper rate can slightly accelerate ammonification and inhibit denitrification in the soil,and yet does not affect much microbial biomass in the soil.