The possible impacts on nitrogen-cycle in a p-nitrophenol (PNP) polluted soil and the effectiveness of wastewater sludge amendments in restoring nitrification potential and urease activity were evaluated by an incubation study. The results indicated that PNP at 250 mg/kg soil inhibited urease activity, nitrification potential, arginine ammonification rate and heterotrophic bacteria counts to some extents. After exposure to PNP, the nitrification potential of the tested soil was dramatically reduced to zero over a period of 30 days. Based on the findings, nitrification potential was postulated as a simple biochemical indicator for PNP pollution in soils. Nitrogen-cycling processes in soils responded positively to the applications of wastewater sludges. A sludge application rate of 200 tons/ha was sufficient for successful biostimulation of these nitrogen processes. The microbial activities in sludge-amended, heavy PNP-polluted soils seemed to recover after 30-45 days, indicating the effectiveness of sludge as a useful soil amendment.