BackgroundIt has been noticed that failure of composite resin restorations can be attributed to either of the two following causes: fracture or secondary caries. For that reason, it is mandatory to formulate a restorative material with antibacterial effect. An octenidine dihydrochloride (OCT) has been assessed as an alternative to antimicrobial material, such as chlorhexidine due to their higher microbicidal effect and less cytotoxicity.ObjectiveCurrent study aimed to add different concentrations of octenidine dihydrochloride into experimental flowable resin composite and evaluate its antibacterial activity over different periods of time to provide the manufacturers with more precise information.MethodsA flowable resin composite material mix was formulated. Octenidine dihydrochloride antibacterial material was then added separately to the formulated mix at 1% wt. and 1.5% wt. concentration, respectively. Antibacterial activity was assessed against Streptococcus mutans using agar diffusion test and compared to a commercial resin composite.ResultsIt showed that by increasing the percentage of incorporated octenidine dihydrochloride (1% and 1.5%), respectively, the antibacterial efficacy against the Streptococcus mutans increased. Results of this study also showed the time had a significant decrease in the antibacterial effect.ConclusionsIt can be concluded that by the incorporation of octenidine dihydrochloride (1% and 1.5%), respectively, the antibacterial efficacy against the Streptococcus mutans increased. Time had a significant decrease in the antibacterial effect of OCT.