A process for preparing 2-(chloromethyl)phenylacetic acid derivatives of the formula I, where X is C1-C4-alkoxy or methylamino, by ether cleavage of compounds of the formula II, where R is C1-C4-alkyl, C1-C4-alkoxy, C1-C2-haloalkyl, C1-C4-alkylcarbonyl, C1-C4-alkylcarbonyloxy, halogen, nitro or cyano; n is 2 to 5; and X is as defined above comprises carrying out the reaction in the presence of hydrogen chloride and an inert solvent, and adding a catalyst to the reaction mixture selected from the group consisting of iron, indium and halides, oxides and triflates, thereof.