PURPOSE:To increase the yield of the objective compound, by isomerizing a dichlorotoluene isomer mixture other than the objective compound or containing the objective compound using a catalyst composed of an acid-type crystalline aluminosilicate zeolite having a specific X-ray diffraction pattern. CONSTITUTION:One or two compounds selected from 2,4-, 2,5- and 3,4-dichlorotoluenes of formula (one of X, Y and Z is CH3 and the others are Cl) are produced by isomerizing a mixture of dichlorotoluene isomers other than the objective dichlorotoluene or containing the objective isomer using a catalyst comprising an acid-type crystalline aluminosilicate zeolite exhibiting an X-ray diffraction pattern having peaks at 11.2+ or -0.2, 10.1+ or -0.2, 3.86+ or -0.08, 3.72+ or -0.08 and 3.66+ or -0.08 in terms of lattice spacings d(Angstrom ). The content of the objective isomer can be increased by this process. The isomers of formula in the six isomers of dichlorotoluene can be selectively isomerized by this process.
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