A semi-organic nonlinear optical L-proline dimercuricchloride (LPDMC) material has been synthesized. LPDMC single crystals were grown from aqueous solution by a slow cooling method. Good quality single crystals of size 19 × 6 × 3 mm 3 have been grown over a period of 3 weeks. The grown crystals have been subjected to single crystal X-ray diffraction analysis to determine the cell parameters. The title compound crystallizes in the triclinic system with a noncentrosymmetric space group P1 and with unit-cell parameters a = 7.2742(4) Å, b = 9.4472(5) Å, c = 10.4767(6) Å, α = 108.621(3) • , β = 107.260(2) • , γ = 97.353(2) • and volume = 631.51(6) Å 3 . Optical and dielectric properties of the crystals have been studied. The thermal stability of the crystals was determined by thermogravimetric analysis/differential thermal analysis. The second harmonic generation efficiency of the crystals was obtained by the classical powder technique using a Nd:YAG laser and it is found to be 2.5 times that of potassium dihydrogen phosphate.