Introduction: Nanoparticles are gaining more interest in dentistry for their antimicrobial, physical as well as other properties. This study aimed to evaluate the effect of adding two types of nanoparticles (NPs) on calcium silicate hydraulic cement’ s (CSHC) unique bioactivity and antibacterial properties. Methods and Materials: Biotitania/AgCl NPs were synthetized and characterized for its morphology, types of formed functional groups and crystalline AgCl using field emission scanning electron microscope (FE-SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometer (XRD), Fourier transformation infrared spectroscopy (FT-IR) and thermo-gravimetric analysis (TGA). The former NPs and commercial titania (TiO2) NPs were added (0. 5, 1. 5 and 3-weight %) to commercial CSHS powder. A total of 140 disk-shaped specimens (10 mm×1 mm) were prepared (seven material groups per each test in addition to the eighth cell control group) to evaluate cell viability and alkaline phosphatase activity (ALP) after 3 and 12 days, respectively. All were incubated with mesenchymal stem cells. Antibacterial efficacy against Streptococcus mutans (S. mutans) was evaluated through the bacterial growth curve slopes while being in direct contact with the tested material groups for 18 h. Results: Addition of all NPs percentages had no significant effect (P>0. 05) on cell viability in comparison to positive control CSHC. Commercial TiO2 NPs (0. 5 weight %) had statistically significant lower values (P≤ 0. 05) for bacterial growth curve slope. However, addition of all NPs percentages had significantly improved (P≤ 0. 05) the ALP activity of CSHC with the most prominent effect to 3-weight% biotitania/AgCl NPs. Conclusion: Based on this in vitro study, addition of biotitania/AgCl NPs up to 3-weight% significantly improved the bioactivity of CSHC without having a significant negative impact on its antibacterial efficacy. Interestingly, the addition of commercial TiO2 even in small amounts can significantly improve CSHC antibacterial efficacy.