Semiorganic materials, in general possess high non-linear coefficient and mechanical strength which will be more applicable for device fabrication. Cadmium thiourea sulphate (CTS) and magnesium cadmium thiourea sulphate (MCTS) are better semiorganic materials which find applications in the field of optoelectronics. Single crystals of CTS and MCTS have been successfully grown from aqueous solution by slow evaporation technique using predetermined solubility data. The basic growth parameters of the crystal nuclei of the grown crystals of CTS and MCTS were evaluated based on the classical theory of homogeneous nucleation. The classical nucleation theory makes use of capillarity approximation which has certain limitations. A correction has to be applied for it and the classical nucleation theory has been suitably modified in order to calculate the critical nucleus parameters. (C) 2008 Elsevier B.V. All rights reserved.