Samples of soils low in phosphorus availability were collected from the National Monitoring Base for Purple Soil Fertility and Fertilizer Efficiency for an indoor experiment, which was designed to have 9 treatments, in terms of phosphate application rate (P₂O₅ 0~150 mg kg^-1 ) and had the soil samples incubated for 75 days, after P fertilizer in the form of disodium dihydrogen pyrophosphate was amended. Analysis of the incubated samples shows that the application of a proper rate of P significantly stimulated the growth of nitrifying bacteria and that of a higher rate had a reverse effect. Treatment 20 (P₂O₅20 mg kg^-1) was the highest in number of the bacteria. Potential nitrification rates (PNR) of the soil samples were determined with the aerobic incubation method and the suspension method, separately. PNR increased in all the treatments to a varying extent and Treatment 50 (P₂O₅ 50 mg kg^-1) was found to be the highest in PNR. The effect of phosphorus on soil nitrifying capacity is similar to that on PNR in tendency. However, further study is needed mechanisms of phosphorus application rate affecting soil nitrification.