Background: Biofilm deposit on the composite restoration is a common phenomenon and bacterial growth follows the deposition. The study aims to evaluateStreptococcus mutans(S. mutans) early biofilm formation on the surfaces of various dental composite resins by using the real-time quantitative polymerase chain reaction (qPCR) technique.Materials and methods: Thirty-two discs, where eight discs were in each group of Filtek Supreme Ultra (FSU; 3M, St. Paul, MN), Clearfil AP-X (APX; Kuraray Noritake Dental Inc., Tokyo, Japan), Beautifil II (BE2; Shofu, Inc., Kyoto, Japan), and Estelite Sigma Quick (ESQ; Tokuyama Dental, Tokyo, Japan), were fabricated and subjected toS. mutansbiofilm formation in an oral biofilm reactor for 12 hours. Contact angles (CA) were measured on the freshly fabricated specimen. The attached biofilms underwent fluorescent microscopy (FM).S. mutansfrom biofilms were analyzed using a qPCR technique. Surface roughness (Sa) measurements were taken before and after biofilm formation. Scanning electron microscopy (SEM), including energy dispersive X-ray spectrometer (EDS) analysis, was also performed for detecting relative elements on biofilms.Results: The study showed that FSU demonstrated the lowest CA while APX presented the highest values. FM revealed that condensed biofilm clusters were most on FSU. The qPCR results indicated the highestS. mutansDNA copies in the biofilm were on FSU while BE2 was the lowest (p < 0.05). Sa test signified that APX was significantly the lowest among all materials while FSU was the highest (p < 0.05). SEM displayed areas with apparently glucan-freeS. mutansmore on BE2 compared to APX and ESQ, while FSU had the least. Small white particles detected predominantly on the biofilms of BE2 appeared to be Si, Al, and F extruded from the resin.Conclusion: Differences in early biofilm formation onto various composite resins are dependent on the differences in material compositions and their surface properties. BE2 showed the lowest quantity of biofilm accumulation compared to other resin composites (APX, ESQ, and FSU). This could be attributed to BE2 proprieties as a giomer and fluoride content.