The major failure of dental restorations is caused by dental caries by S. mutans. This study evaluated the effect of nanosized silver ions in feldspathic porcelain on cytotoxicity and antimicrobial activity. The control group was feldspathic porcelain (Noritake EX-3, Kuraray Noritake Dental Inc., Japan) that did not contain Ag (silver). The experimental groups were feldspathic porcelain mixed with colloidal solutions of nanosized silver ions in mixtures of 5% 10%, 20%, 30%. Cell activity assays evaluated with osteoblast hFOB 1.19 cells (human Fetal Osteoblastic cell line, ATCC® CRL- 11372™) and antimicrobial activity test used the streptococcus mutans (S. mutans). According to the observations, the addition of Ag to feldspathic porcelain led to increased cell activity and showed excellent antibacterial performance. Especially, the feldspathic porcelain with 30% nanosized Ag ion appeared to have a significant antimicrobial effect, this allows for the possibility of various clinical applications for such material, including use in dental prosthesis and implants.