Free-, soluble- and insoluble phenolic acids were extracted from defatted Galla Rhois. The extracts were then dissolved in equal amounts of an soybean oil, and POV (peroxide value) of the resulting substrates, portion of the soybean oil (control) and 0.02% BHT were measured by AOM (active oxygen method) test at 97.8$^{circ}C$ for 40 hours through Rancimat method. Induction period of control, BHT, free phenolic acids, soluble phenolic acids and insoluble phenolic acids by the Rancimat method were 4.8, 10.5, 23.9 and 30.5hr. The phenolic acids separated and tentati-vely identified by gas chromatography were catechol, gallic acid, vanillin, protocatechuic acid, syri-ngic acid, ferulic acid.