Au and Au-CdSe nanoparticles (NPs) have been synthesized by organometallic pyrolysis method. Nanocrystals (NCs) structure was confirmed using high resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD). Nonlinear optical absorption is investigated by Z-scan technique using nanosecond laser pulses of second harmonic Nd:YAG. Intensity-dependence of nonlinear absorption on both nano-size and concentrations is reported. These are interesting findings which can be used to fabricate optical limiting and optical switching devices from NPs and hybrid systems. (C) 2015 Elsevier B.V. All rights reserved.