For biomedical applications, various optical techniques have been explored, all of which are inherently subject to the limited penetration depth of observation. Nanoparticles have thus been introduced as a potential agent to overcome the limit and to reveal more information on biomedical samples. Optical properties of nanoparticles in a turbid medium, however, have remained difficult to measure precisely. In this paper, we investigate the scattering and absorbing properties of gold nanoparticles of varying diameter and different concentration in absorbing liquid phantoms of silica colloid, based on diffuse photometry. Diffuse reflectance patterns have been collected for each phantom with nanoparticles of different size and concentrations relative to base media. The results imply that particle concentration and size perturbs the medium properties, and the effect is dependent on the scattering properties of the particle. For the case where the particle size stays within a range, the scattering property is dominated by the concentration.