Abstract: The investigation of phytol interference was carried out by determining fatty acids in herbage using gas chromatography with methyl ester method by catalyzed potassium hydroxide and by saponification Boron trifluoridee, respectively. In order to eliminate the interference of phytol, the method catalyzed by saponification Boron trifluoridee was improved. The results indicated that the phytol interference to the determination of fatty acids in herbage by either of two methods all exist. The interference of phytol in the potassium hydroxide method was more serious than the other. Phytol can be eliminated by Boron trifluoridee-catalyzed after saponification at 80℃. And the esterification efficiency of fatty acid attained the highest value at 80℃ among five classes of temperatures. The spiked recoveries were in the range of 87.5%－94.1% at 100 mg/kg and 500 mg/kg levels; the relative standard deviations (RSD) were in the range of 2.0%－5.1%. The improved method is suitable for the determination of fatty acid in herbage and can eliminate the interference of phytol.