The third order NLO properties of thiourea and its metal complexes were measured using a 532 nm second harmonic of diode pumped Nd:YAG laser (1064 nm, 50 mW) by employing the Z-scan technique. The magnitude of nonlinear refractive index, nonlinear absorption coefficient and third order susceptibility was found to be in the order of 10(-8) cm(2) W-1, 10(-3) cm W-1 and 10(-8) esu respectively. The Z-scan reflects the negative nonlinearity of the samples and hence self defocusing nature is responsible for the optical limiting behavior in the regime of interest. The response time was found to be in the order of milliseconds. (C) 2011 Elsevier BM. All rights reserved.