Large pore faujasite zeolite (Pt/H-Y) and its dealuminated form (Pt/H-DY) were applied for transalkylation of toluene and 1,2,4-trimethylbenzene (1,2,4-TMB). The acidic properties of supports were examined by using NH3- TPD and FT-IR spectroscopy in the OH stretching region. XRD, SEM, DSC and FT-IR in the framework region techniques were employed to investigate the structural changes of zeolite after dealumination process. It was observed that the dealuminated catalyst tends to have more open structure; such structural changes are believed to compensate for the loss of some acid sites to bring about the enhanced activity and stability over the parent zeolite. The zeolite structure has a direct influence on aromatics conversion. It was found that the use of 1,2,4- trimethylbenzene (TMB) as an alkylation agent gave the highest yield of xylenes. A strong competition between transalkylation, disproportionation and isomerization of aromatic hydrocarbons takes place according catalyst acidity and reaction temperature.