The catalytic properties of zeolite NU-87 were investigated with respect to the disproportionation of 1,2,4-trimethylbenznen and the results were compared to those obtained over H-beta and H-mordentie with 12-membered ring channel system. In the conversion of 1,2,4-trimethylvenzene, the disportionation to xylene and tetramethylbenzene is preferred to the isomerization into 1,2,3- and 1,3,5-isomers over all the three zeolites, but this trend is much more pronounced over HNU-87 owing to its peculiar pore structure. Disproportionation reaction is found to proceed within the micropores of HNU-87, whereas isomerization occurs mainly on the external surface. The high selectivity to disproportionation gives more xylenes and tetramethylbenzenes over HNU-87. The detailed descriptions for the product distribution are also reported.