Abstract: A sensitive method for the determination of pyraclostrobin and its metabolite BF-500-3 in longan (Dimocarpus longan Lour.) was developed based on high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) technique. According to “Guideline for the testing of pesticide residues in crops”, field tests conducted in Guangzhou City of Guangdong Province and Yuxi City of Yunan Province. The residual behavior of pyraclostrobin parent and its metabolite based on longan field trials was investigated. The results showed good average recoveries of 84%-96%, with relative standard deviations of 3.8%-6.7%, at the spiked levels of 0.001, 0.1 and 2 mg/kg in longan. The limit of detection (LOD) was 0.25 × 10⁻³ mg/kg and the limit of quantification (LOQ) was 0.001 mg/kg. When pyraclostrobin was applied 3-4 times at the dosage of 375 mg/kg with the interval period of 7-10 days, and pre-harvest interval of 5, 7 and 10 days, the residues of pyraclostrobin parent and BF-500-3 in longan were 0.11-0.72 mg/kg and 0.011-0.071 mg/kg, respectively. This study would be helpful to guide the scientific and efficient utilization of this fungicide. Because of the absence of maximum residue limit (MRL) of pyraclostrobin in longan, these results could provide references to facilitate the setting of MRL of pyraclostrobin.