The purpose of this study was to investigate the effects of filling and lining materials in various compositions on Streptococcus mutans. Five glass-ionomer cements (Vitrebond, XR Ionomer, Ketac-Bond, Shofu Base Cement, Shofu Lining Cement) and two composite materials (Heliomolar-RO, Concise) were used in this study. Samples from these materials were prepared in sterilized conditions and hung in tryptic soy broth medium containing 5% sucrose. The media were inoculated with Streptococcus mutans ATCC 13419. After 5 days, the plaque that had accumulated on the surfaces was scraped off and weighed in wet and dry conditions, Then the colonies were counted and evaluated in comparison with each other. The least amount of plaque and colony numbers were found on Vitrebond material disks, in conclusion, there were no differences among XR Ionomer, Heliomolar-RO and Ketac Bond. Concise gave better results than some materials containing fluoride; whereas the most abundant amounts of plaque were found on Shofu Lining Cement and Shofu Base Cement.