Nonlinear optical single crystal of tetrathiourea mercury (II) tetrathiocyanato manganate (II)-Hg(N2H4CS)(4)Mn(SCN)(4) (TMTMj`was conveniently grown by slow evaporation technique. The cell parameters of TMTM single crystals were confirmed by single crystal Xray diffraction. The grown crystals were subjected to optical characterization by FT-IR, FT-Raman and UV-vis-NIR techniques. Thermal studies suggest that TMTM undergoes three stages of decomposition and is thermally stable up to 199.06 degrees C. (c) 2007 Elsevier B.V. All rights reserved.