Abstract: Residues of fipronil and its metabolites in paddy-fish soil were detected using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Samples were extracted with oscillation and acetonitrile in constant temperature, and subsequently purified by solid phase extraction using ENVI-18 column and 10 mg GCB. The target compounds were separated on an Agilent ZORBAX Extend-C18 column (2.1 mm×100 mm×1.8 μm), and determined using electrospray ionization (ESI) source at negative mode with multiple reation monitoring (MRM). The analytes were quantified with external standard using the matrix-matched standard calibration curve method. The results indicated that the average spiked recoveries of fipronil, fipronil-desulfinyl, fipronil-sulfone and fipronil-sulfide in paddy-fish soil were 83.5%-110.3% with the relative standard deviations (RSDs) of 1.9%-11.5%. Good linearities were obtained in the range of 0.5-100 μg/L, and the correlation coefficients were greater than 0.998, the limits of detection (LODs) were 1.0 μg/kg, and the limits of quantification (LOQs) were 3.0 μg/kg. This method is simple, accurate and reliable, which can meet the detection requirements of fipronil and its metabolites in paddy-fish soil.