Abstract: GC-MS was applied to the determination of residual amount of m-xylylene diisocyanate in food contact materials of PET plastic. The sample (1.000 g) was extracted ultrasonically with 5 mL of ethyl acetate for 25 min, and then the supernatant was diluted to 10 mL with ethyl acetate. The above sample solution was taken and filtered on 0.45 μm organic microporous filter membrane. The HP-5MS quartz capillary chromatographic column was used for GC separation and the full scanning mode and the selected ion monitoring mode were adopted in MS determination. Linear relationship between values of peak area and mass concentration of m-xylylene diisocyanate was kept in the range of 0.05-5.0 mg·L^-1, with lower limit of determination (10S/N) of 0.05 mg·kg^-1. On the base of blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 79.2%-93.4%, with RSDs (n=7) in the range of 0.83%-4.5%.