Abstract: The nature of selenium-sulfur non-bonding interactions in a series of substituted benzeneselenenyl derivatives has been investigated by means of computational techniques. The results of these calculations, together with experimental measurements (X-rays crystallography and NMR), suggest that the strength of this interaction increases with the increase of electronegativity of the substituent on selenium. Natural bond orbital (NBO) analysis suggests that this interaction has a mainly covalent character, rather than electrostatic, and originates from an interaction between a lone pair of sulfur and an antibonding orbital on selenium. Atom in molecules (AIM) analysis further supports this finding.