Bisthiourea zinc bromide (BTZB), a novel semi-organic NLO material, has been synthesized and characterized by X-ray diffraction, FT-IR absorption and electron diffraction techniques. Single crystals of BTZB with size in the range 5 x 4 x 3 mm(3) have been grown from aqueous solution by slow evaporation method. Thermal analysis has been performed on the material to study its thermal stability in the temperature range 303 K-1073 K. BTZB belongs to the category soft materials as evidenced by Vicker's microhardness tests. The material has lower dielectric constant (14.1) than its parent molecule thiourea (15.6). From optical absorption and photoluminescence spectra, the band gap has been determined to be 3.5 eV. The nonlinear optical properties have been investigated by Z-scan method and the material is found to be self-defocusing in nature. In this paper we report the optical limiting behavior in the low-power regime for the first time in literature using a 532 nm second harmonic of a diode pumped Nd: YAG laser. (C) 2010 Elsevier B.V. All rights reserved.