A Monte Carlo (MC) lattice gas model of adsorption of a racemic mixture of enantiomers of 1,2-dimethyleyclopropane on a chiral surface with different spatial distribution of active sites was proposed. The calculations were performed on a square lattice for both stepped chiral surfaces and smooth surfaces with chiral patterns of active sites. The adsorbing molecules were assumed to be rigid structures of two types being mirror images one of another. Regardless of the enantiomer type, each molecule was composed of four segments occupying four lattice sites. The chiral surfaces were exposed to equimolar mixture of enantiomers whose individual equilibrium adsorption isotherms were calculated using standard Grand Canonical MC technique. The major purpose of the simulation was to examine how the structure of the surface affects separation of enantiomers., that is, to determine enantioselectivity defined as the ratio of their adsorbed amounts. Additionally, comparison of the enantioselectivities corresponding to the stepped and smooth surfaces was made. (C) 2006 Elsevier B.V. All rights reserved.