Silver nanoparticles (AgNPs) with antimicrobial property have been used for years in various applications, such as antibacterial coating and air/water purification to eliminate microorganisms. In recent years, a number of studies on the potential risk of nanomaterials in humans and the environment have appeared, and thus a large number of studies regarding the toxic effects of AgNPs on cells and micro-organisms have been reported. In in-vivo and invitro cytotoxicity tests, various biological media are used, and thus the dispersion stability of AgNPs in media is important to a successful toxicity test. Therefore, we investigated the dispersion stability of AgNPs in various biological media; PBS (phosphate buffered saline), FBS (fetal bovine serum), and de-ionized water (pH 2, 7, and 9) with and without photo-irradiation. Herein, citrate and PVP (polyvinylpyrrolidone) stabilized AgNPs were used as target materials. In short- and long-term stability tests, we found that PVP-AgNPs stabilized by steric hindrance have good dispersion stability in biological media, compared to citrate-AgNPs stabilized by electrostatic repulsion.