Nucleation parameters such as solubility, induction period, interfacial energy and nucleation rate and critical radius, Gibbs free energy change, number of molecules in the critical nucleus have been investigated for the aqueous solution growth of a semi-organic nonlinear optical (NLO) material of L-Leucine doped Zinc Tris-thiourea sulfate (ZTS). From the results, it was observed that the induction period increases with increase in additive concentration L-leucine into ZTS solutions. The critical nucleation parameters such as radius of critical nucleus, Gibbs free energy change and number of molecules (n) in the critical