This study was carried out to develop an extraction as well as an analytical method for detecting benzobicyclon and its amino-substituted metabolite (1315P-570) in brown rice and rice straw using liquid chromatography-tandem mass spectrometry (LC/MS/MS) in positive ion mode with multiple reaction monitoring (MRM). The parent as well as the metabolite in rice and rice straw were extracted and analysed under the same conditions. A correlation coefficient (R(2)) of >0.994 was obtained for matrix-matched calibration curves constructed in various concentration ranges. Recoveries at two fortification levels were satisfactory and ranged between 75.4% and 118.9% with relative standard deviations (RSDs)<13%. Under storage conditions (-20°C), the analyte and its metabolite were stable for up to 92days. The limits of quantitation (LOQ) were lower than the maximum residue limit (MRL) (0.1mg/kg) set by the Korea Food and Drug Administration for brown rice. Field trials with recommended or double the recommended dose revealed that the herbicide could safely be applied to rice and rice straw, as no residues were detected in the harvested samples. The sensitivity of the developed method was sufficient to ensure reliable determination of benzobicyclon and its metabolite in rice grain and rice straw.