Nanotechnology presents countless opportunities to develop new and improved consumer products for the benefit of the society . A most prominent nanoproduct is nanosilver. Nanosilver particles are generally smaller than 100 nm and contain 20–15,000 silver atoms. Despite the wide application of nanomaterials, there is a serious lack of information concerning their impact on human health. In the previous study we reported the cytotoxic of nanosilver on osteoblast G292 cancer cell line and the amount of IC₅₀ determined as 3.42 µg/ml (Moaddab et al., Iran. Nano Lett., Vol. 1, No. 1, January 2011, pp. 11-16). The purpose of the present study is to assess the biological assay of nanosilver on two normal cell lines of fibroblast (HF2), and mesenchymal stem cells . The effect of nanosilver on these cells is evaluated by light microscopy, and by cell proliferation and standard cytotoxicity assays. The results demonstrate a concentration-dependent toxicity for the cells tested, and IC₅₀ was determined as 6.33, and 6.68 µg/ml in mesenchymal stem cell, and fibroblast HF2, respectively. There is no significant difference between the 24 h and 48 h of cells exposure to nanosilver. The results show that Nano-Ag possesses low toxicity to normal cells and can display potential application in cancer chemoprevention and chemotherapy.