The potential of herbicides for nonpoint ground water pollution depends on their degradation behavior in soil.The present study was conducted to investigate the degradation of napropamide in soil under different conditions.The rate of napropamide degradation in soil was determined by extracting and detecting residual levels over a 60 d incubation period.In the five tested soils, degradation profile of napropamide followed the first-order kinetics.Soil organic matter (OM) greatly facilitated degradation of napropamide.The degradation rate of napropamide in soil increased with increasing temperature.Half-lives (T1/2) values ranged from 51.7 d at 35 ℃ to 93.6 d at 10℃.Soil moisture content influenced the herbicide degradation in the following order: 80 > 60 > 40 >20% water holding capacity (WHC).The prolonged T1/2 by sterilization showed that microorganisms were the predominant contributors to degradation of napropamide in soil.The degradation of napropamide declined as the initial concentration increased.The results suggest that to reduce translocation to surface and ground water, this herbicide application should be conducted at a minimum effective application rate considering environmental factors, especially soil OM, temperature and moisture.