A potentially useful second harmonic generation (SHG) organometallic nonlinear-optical crystal, MnHg(SCN)(4)(C2H6OS)(2) (MMTD), has been prepared, and high optical quality single crystals up to 25 x 18 x 18 mm(3) in size have been successfully grown by the slow temperature-lowering technique. Its structural, physicochemical and optical properties have been characterized using elemental analyses, infrared spectroscopy, thermal analysis, SHG measurements and VIS/UV/NIR spectroscopy. The material possesses a good physicochemical stability up to 145 degreesC and exhibits powder SHG efficiencies about 23 times that of urea. The UV transparency cutoff is 375 nm, and the transmission is 44.81% at 404nm, which is 17.45% higher than that of MnHg(SCN)(4) (MMTC).