Abstract: The pulverized tea sample was extracted three times for 10 min with water in 90℃ water bath. Volume of the combined extract was made up to 50 mL with water. 1.00 mL of the above solution was filtered on 0.22 μm filtering membrane. Hydrophilic interaction liquid chromatography with tandem mass spectrometry was applied to the determination of γ-aminobutyric acid and theanine in the filtrate. Waters Atlantis HILIC NH₂ chromatographic column was used as stationary phase, and the mixture of water and acetonitrile (9+1) solution (containing 2 mmol·L^-1 ammonium acetate and formic acid with 0.1% volume fraction) mixed in different ratios was used as mobile phase in gradient elution. ESI⁺ and multi-reactions monitor mode were adopted in MS/MS. Linear relationships between values of peak area and mass concentration of γ-aminobutyric acid and theanine were kept in the same range of 5.00-500.00 μg·L^-1, with detection limits (3S/N) of 1.00, 0.50 μg·L^-1, respectively. The proposed method was applied to the analysis of tea samples, giving values of recovery found by standard addition method and RSDs (n=9) of determined values in the ranges of 97.8%-107% and 4.9%-7.1%, respectively.