A facile one step synthesis approach for preparing Ag@SiO2 core-shell nanoparticles was reported and its third-order nonlinear optical analysis was discussed. The linear optical behaviour of the synthesized core-shell structured Ag@SiO2 nanoparticles was studied by UV-vis spectral analysis. The red shifting of the surface plasmon resonance peak affirmed the core-shell structure of the products. The surface functionality of the product was probed by the FTIR spectral investigations and the results revealed that silica networks formed an outer shell covering Ag nanoparticles. The crystallinity and chemical composition of the products are analyzed by powder XRD pattern and confirmed that the crystallinity of Ag nanoparticles was not affected by the formation of the amorphous SiO2 shell. The particle size, morphology and the formation of uniform SiO2 shell over the Ag core are visualized by the TEM analysis. Moreover, the optical nonlinearity of the Ag and Ag@SiO2 core-shell nanoparticles is examined by z-scan technique using continuous wave He-Ne laser which showed interesting optical nonlinearity and exhibited switching behaviour from reverse saturated absorption to saturated absorption, which could be useful for numerous photonic applications like, Q-switching and optical limiting. (C) 2018 Elsevier B.V. All rights reserved.