Abstract: Intermolecular interactions in nano-porous crystals were studied theoretically as related to adsorption properties. The crystal [Rh2bza4pyz] n , which had been reported by Mori, Takamizawa and their co-workers in detailed, was employed in this study. As adsorbed magnetic radicals, a oxygen molecule (O2; S =1) was treated. Adsorption energies ΔE ads are defined for quantitative discussion for host–guest interaction. From the calculated results by our MO calculations, weak attractive interactions between adsorbed O2 and surrounding four ph-groups (delegated to benzene) existed. In addition, stable structure of O2 molecules over one benzene molecule was studied. From the results, parallel structure is more stable than perpendicular structure. Physisorption phenomena in intermediate distance region (R =3.4Å) contributes to energy stabilization. [Copyright &y& Elsevier]