Good optical grade single crystals of pure, Cd 2+ and Mg 2+ doped Manganese Mercury Thiyocyanate (MMTC) crystals are grown by slow solvent evaporation technique at room temperature. Single crystal XRD studies reveal that the incorporation of metallic dopants has not changed the structure of the parent crystal. The SHG efficiencies of the pure and doped samples of MMTC are measured by Kurtz Perry powder method and the results are compared with urea. It is evident from microhardness study that the presence of dopants has increased the mechanical strength of MMTC crystal. The TG/DTG studies confirm that the thermal decomposition temperatures of pure (353°C), Mg 2+ doped (363°C ) and Cd 2+ doped (365°C) MMTC are relatively high when compared to other NLO crystals of the same family.