During the last decade, the usage of silver nanoparticles in biomedical fields has increased rapidly, mainly due to their excellent antibacterial effects. They are used in many medical products such as wound dressings, catheters, bone cement and artificial cardiac valves. In tissue engineering, silver nanoparticles are often loaded as a filler for fabrication of nanocomposite scaffolds which subsequently are seeded with human mesenchymal stem cells. Thus, possible adverse effects of silver nanoparticles on human stem cells should be investigated carefully to ensure a safe usage. In this study, silver nanoparticles with a mean diameter of ~30 nm were prepared and their toxicity in human mesenchymal stem cells was investigated. Transmission electron microscopic images reveal the uptake and localization of the silver nanoparticles in the cytoplasm. Upon internalization of Ag NPs inside the cells, an increase in the release of lactate dehydrogenase and the production of reactive oxygen species was quantified. Furthermore, they caused a reduction in both cell viability and mitochondrial membrane potential in a dose-dependent manner. Annexin V-FITC/PI staining implied that silver nanoparticles did not only induce apoptosis but also cause necrosis. Based on cell cycle analysis, G2/M arrest was detected in cells treated with silver nanoparticles, implicating DNA damage. The high level of reactive oxygen species induced by nanoparticles is considered to be the main cause of their toxicity.