Grand canonical Monte Carlo simulation of sorption of nitrogen and oxygen has been carried out on LiLSX zeolite structures and accurate adsorption data was measured on LiLSX powder using the isosteric technique. The position of Li cations in the LiLSX structure was predicted using the MSI Cerius(2) cation locator module. Simulation of sorption on various structures of LiLSX, which contain Li cations at different locations, indicate that sites SIII and SIII＇ show similar interaction energies and that Li cations in site SnII are not involved in the sorption process. The simulated values for sorption capacity, N-2/O-2 selectivity and isosteric sorption heat are in good agreement with experimental data. The simulated values of sorption capacity and isosteric sorpation heat on the predicted structures are also close to those obtained on structures built by using crystal structure data and the experimental sorption data obtained at low pressures.