Objective To establish a gas chromatographic-mass spectrometric （GC-MS） analysis method for quantifying 1-methylhydantoin concentration in whole blood. To provide technical support to forensic identification related cases of 1-methylhydantoin. Methods As an internal standard, 500 ng SKF525A was added to 0.5 mL blood sample, and then 2 mL 0.01 mol/L dilute hydrochloric acid and 0.5 g ammonium carbonate were added in order to buffer the pH value to 9, and following 2 mL ethyl acetate. The organic solvent layer was obtained after centrifuge and then analysed by GC-MS after drying. Results Good linear relationship of 1-methylhydantoin in blood was obtained in the range of 0.5-50 ng/mL. The equation of linear regression was y=0.015 51 x+0.007 26（R2=0.999 7） with 0.1 ng/mL detection limit, and the recovery was 93.02%-108.12%. The intra-day and inter-day precision were less than 6.07% and 13.37%, respectively. Conclusion The results gotten by this method is accurate and reproducible, which can be used for the determination of 1-methylhydantoin concentration in blood samples.