Abstract: The powder sample of orange juice was extracted with DMF and separated by centrifugation.Ascorbic acid in the supernatant was derivatized with hexamethyldisilazane and trimethylchlorosilane,and the derivatized product were extracted with n-heptane.The extract was used for GC-MS analysis after adding methyl hexadecanoate (or methyl palmitate) as internal standard.The HP-5MS capillary column was used for GC separation and the full-scanning mode was adopted in MS determination.Linear relationship between values of peak area ratios of the ascorbic acid standard to internal standard and mass of ascorbic acid was obtained in the range of 1.0-5.0 mg.The proposed method was applied to the determination of vitamin C in the powder sample of orange juice,giving the average mass fraction (n=6) of vitamin C 0.195 4% and values of recovery in the range of 92.3%-98.5%.