This paper describes a methodology used to study sorption properties of molecules in zeolites. The method involves a combination of computer simulation techniques and quantum chemical calculations. As a specific example, the results of the calculations for the adsorption of methanol molecule in ZSM-5 zeolite are reported. The interaction energy of the methanol molecule with the framework atoms of the zeolite is calculated, as the methanol moves along the straight channel. The favourable adsorption sites are deduced based on the calculated values of the interaction energy. Non-empirical quantum, chemical calculations have been performed on the ZSM-5: methanol adsorption complex and its dissociation mechanism is proposed based on the results.