In this work, Ag nanoparticles in polyvinylpyrrolidone (PVP) solution at different concentrations have been prepared using gamma-radiation method. A single beam Z-scan method with an excited laser beam 532 nm wavelength and an output power of 50mW, applied for measuring the nonlinear refraction and absorption coefficient of samples. The sign of the nonlinear refractive index shows a self-defocusing phenomena happened in this measurements and also the magnitude of nonlinear refraction and absorption are in order of 10^-8cm²/W and 10^-3cm/W, respectively. The measurements show that the optical susceptibilities of the samples tend to be increased with increasing of the concentration of Ag nanoparticles. Ag nanoparticles can be promising in different aspects of applied optics and optical devices.