A selective, sensitive gas chromatography-mass spectrometry (GC-MS) method with negative chemical ionization (NCI) was developed for the detection and quantification of clopidol in chicken muscle. Chicken muscle samples were extracted with acetonitrile and concentrated to dryness; the residue was redissolved in ethyl acetate and applied to an Alumina B cartridge for cleanup. The residue was derivatized with Sylon BFT and analyzed by GC-NCI-MS. The selected-ion monitoring mode was performed at m/z values of 156, 158, 191, and 193. The differences in the ratios for the standards and spikes in chicken muscle were within the acceptability criteria. All recoveries of the drug from chicken muscle spiked at 0.5, 5.0 and 50.0 microg/kg were 74.5-95.6% intra-day, and 71.6-94.8% inter-day, respectively, with relative standard deviations being lower than 15%. The limits of detection and quantitation were 0.1 and 0.5 microg/kg, respectively. The NCI mode had better selectivity and sensitivity than the electron impact (EI) mode for clopidol.