Abstract: The sample of 0.500 0 g was placed into a baker of 10 mL, and adjusted to pH 8-9 with 0.1 mol·L^-1 KOH-methanol solution. Water in the sample was concentrated to dryness at 100℃.The residue was dissolved in 10 mL of sulfuric acid-methanol (5+95) solution and esterification reaction was taken for 30 min at 70℃. Then the reacted solution of 200 μL was extracted with dichloromethane of 1 mL as the extraction solvent in a self-designed micro liquid-liquid extraction device, and water of 1 mL was added to oscillate. n-Butyric acid and lactic acid were determined by gas chromatography-mass spectrometry (GC-MS). As shown by the results, Linear relationships between values of peak area and mass concentration of n-butanoic acid and lactic acid were found in the range of 0.10-50.00 mg·L^-1, with detection limits (3S/N) of 0.1 mg·kg^-1 for n-butanoic acid and 0.4 mg·kg^-1 for lactic acid. Test for recovery was made by standard addition method, giving results in the range of 97.7%-108%, with RSDs (n=5) ranged from 0.60% to 12%.