We design some experimental setups to investigate optical properties of plasmonic nanoparticles, namely absorption and scattering cross section. Light emitting diode and xenon lamp are used as light sources to cover the desirable spectrum region. To evaluate the results of the proposed technique, we measure the size of Silver and Gold nanoparticles synthesized by chemical reduction method. Having absorption and scattering spectra, we employ Mie theory to determine size of the nanoparticles. The size of nanoparticles is in the range of 10 to 60 nm. Then compare results with the results obtained from Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM) techniques. The comparison confirms that the proposed methods are accurate enough to be used for investigating optical properties of plasmonic nanoparticles. And the results are in good agreement with the actual size. And results show that the scattering peak of gold and silver nanoparticles are in the ultraviolet-visible range.