Abstract: (1) The condensation of guaiacol with acetic anhydride using polyphosphoric acid (PPA) as catalyst gave either acetovanillone (Ⅰ) or the acetate of isoacetovanillone (Ⅱ), depending on the amount of acetic anhydride used. Our hypothesis on the reaction process was confirmed by experiment. (2) Using PPA as catalyst, the ester of α-chloro acetyl guaiacol did not undergo the Fries rearrangement. This phenomenon is interpreted as due to the electron-withdrawing power of the chlorine atom. (3) When the phenolic group of guaiacol was blocked by α-chloro-acetyl group, 3-hydroxy-4-methoxy-phenyl alkyl ketone (Ⅴ) could be obtained in excellent yield.