The preparation of tetrathioureamercury(II) tetrathiocyanatozinate(II), Hg(N2H4CS)(4)Zn(SCN)(4) (abbreviated as TMTZ) crystals is described. The characterization of the synthesized compound has been performed by X-ray powder diffraction, infrared, Raman and UV/Vis/NIR transmission spectroscopy and powder second harmonic generation efficiency measurement. The thermal stability and thermal decomposition of TMTZ crystal have been investigated by means of thermogravimetric analysis and differential scanning calorimetry measurements. The UV transmittance and the SHG efficiency of TMTZ are both inferior to those of ZMTC. Under nitrogen flux, its melting point is 180.7degreesC and its thermal decomposition starts at 191.5degreesC. (C) 2004 Elsevier B.V. All rights reserved.