Batch sorption experiments were conducted for a paddy soil in Taihu Lake region to measure napropamide sorption of bulk soil samples and particle size fraction samples separated by ultrasonic dispersion method. Results showed that adsorption isotherm of napropamide can be described well by the Freundlich eqation, and coefficient Kf values ranged from 5.56 to 11.40. Higher K_f values was found in <0.002 mm and 2.00~0.25 mm size fractions. While taking into consideration of composition of soil size fractions, contribution of <0.002 mm size fraction was highest for napropamide. It suggested that potential negative effect of napropamide on environment couldn't be neglected because napropamide could migrate more easily in soil-water environment via sorption from soil fine-size particles.