The structures and properties of osmabenzyne and para-substituted osmabenzynes (X=F, Cl, Br, Me, NH 2 , OH, NO 2 , CHO, COOH) have been explored using theoretical methods. Frontier orbital analysis indicates the HOMO and LUMO are distributed on the ring carbon atoms, Os and Cl ligands. Time dependent density functional theory (TD-DFT) is used to calculate the energy, oscillatory strength and wavelength absorption maxima (λ max ) of various electronic transitions and their nature within molecules. Non linear optical (NLO) behavior of title compounds is investigated by the computed value of first hyperpolarizability (β total ).