Array structures and molecular orientations within liquid-phase-adsorbed pyridine base (pyridine and beta-picoline) adlayers on (010) surfaces of two natural zeolites (stilbite and heulandite) that have been observed by atomic force microscopy (AFM) were simulated by means of molecular mechanics (MM2＇) calculations. For the beta-picoline/stilbite system, present calculations indicated that an edge-on molecular orientation with the 6-C-N bond parallel to the surface is most likely, in accordance with previous AFM observations, but in contrast to a common expectation. While AFM was not able to determine molecular orientations within the adlayers of pyridine/heulandite system, the present simulation showed the N corner-on configuration to be the most stable one. Intralayer molecular interaction and molecule-substrate interaction energies were found to be of comparable value for these adsorption systems. Adsorption registries and adlayer-substrate distances, which were not determined by AFM, were also estimated.