Abstract: A qualitative and quantitative method using UPLC-MS/MS was developed for the analysis of penoxsulam residues in rice paddy samples including rice plant, paddy water, soil and brown rice. The residue and dissipation of penoxsulam in the rice paddy were investigated for dietary risk assessment of residual penoxsulam in brown rice. Based on the analytical approach, the satisfied linearity was obtained in the concentration ranged from 0.005 mg/L to 0.5 mg/L with the limit of detection(LOD) from 0.001 mg/kg to 0.002 mg/kg and the limit of quantification(LOQ) from 0.003 mg/kg to 0.005 mg/kg. With the spiked concentrations of 0.005 to 0.5 mg/kg, the average recoveries varied from 89% to 106% with the relative standard deviation (RSD) from 2.8% to 8.5%. Those results indicated that this new method has favorable accuracy, precision and sensitivity, which meets the demand of pesticide residue analysis and is applicable for effective monitoring the penoxsulam residual in rice paddy field. The results of residue dynamics indicated that the half-lives of penoxsulam in rice plant, paddy soil and water were 1.5-3.3 d, 3.0-4.7 d, and 1.6-3.0 d, respectively. Hence, penoxsulam belongs to a class of readily-degradable herbicide in the rice paddy environment. After the application of 0.025% penoxsulam granules twice with the dosage at 37.5 g a.i./hm² and 56.3 g a.i./hm², respectively, the highest residues of penoxsulam in brown rice were lower than 0.005 mg/kg and the dietary risk was low in which the risk quotient was 2.22×10^-4, which was obviously lower than risk threshold. Taken together, our data can be used as an important methodological and statistical basis for the further integrated evaluation of dietary risk and MRL formulation.