In the case of acylation reaction of aromatic hydrocarbons it is observed that acylation of toluene and naphthalene in the presence of acidic zeolites such as H-ZSM-5, H-ZSM-12, H-Beta, H-Mordenite, and H-Y results in different products with variable selectivities. It is observed experimentally that benzoylation of toluene and naphthalene over zeolite H-Beta follows the selectivity order: 4-methylbenzophenone > 2-methylbenzophenone > 3-methylbenzophenone and 2-benzoylnaphthalene > 1-benzoylnaphthalene, respectively. Zeolite H-Beta shows the best selectivity among all other acidic zeolites. To explain this selectivity order a computer simulation study has been performed. Molecular mechanics were used to calculate the individual strain, dimensions of reactant, and product molecules; the dimensions of zeolite cages were compared. The results show that zeolite Beta is the best zeolite in terms of fitting of the reactant and product molecules. DFT was applied to study the electronic property and interaction energy of reactant and product molecules with acidic zeolite framework to rationalize the mechanism of acylation reaction over acidic zeolites. Molecular electrostatic potential maps were also plotted from DFT to rationalize the polarization of the reactants in the reaction process. The results were compared with experimental observation which justifies the role of acidic zeolites, in this particular reaction.