Abstract: A method of GC-MS/MS for the determination of residual amount of caprolactam in nylon 6 resin and its mouldings was proposed. The sample was smashed by freezing milling and extracted ultrasonically with methanol, and the extract was concentrated to 1 mL by N2-blowing. DB-WAX column was used for separation, and MS/MS was used for determination. Linear relationship between values of peak area and mass concentration of caprolactam was obtained in the range of 0.005-5.0 mg·L-1, with detection limit (3S/N) of 0.002 mg·kg-1. Recovery was tested by addition of caprolactam standard solution at 3 concentration levels, giving values of average recovery and RSD′s (n=6) in the ranges of 88.8%-101% and 3.2%-7.0% respectively.