The nonlinear optical (NLO) absorption and refraction properties of different nanostructures, such as ZnS nanosheets, ZnS-ZnO composite and porous ZnO nanostructures, dispersed in de-ionized water, are reported by performing the z-scan technique with 532 nm ns pulsed laser radiation. The values of NLO coefficients of the materials are extracted from the experimental z-scan data. The two-photon induced free carrier absorption has been observed in the samples. The experimentally obtained two photon absorption coefficient of ZnS-ZnO nanocomposite is an order-of-magnitude larger that of ZnS nanoparticles. The presented results may open up new possibilities of using these materials in different NLO devices. (C) 2013 Elsevier B.V. All rights reserved.