>Magister Scientiae - MSc / Nanotechnology has emerged as an elementary division of modern science and stemmed directly from green chemistry twelve basic concepts, it receives global attention due to its unique character and ample applications. It also has great potential to mitigate the challenges they face in various fields, especially medical sector. Nanodrugs are increasingly considered as a potential candidate to carry therapeutic agents safely into a targeted compartment in an organ, particular tissue or cell. In this study, twenty (20) Libyan plants were selected and evaluated for their potential to synthesis gold and silver nanoparticles. The screening of the different plant extracts was performed using 96 well plate method at 25 °C and 70 °C. The NPs formation was confirmed and characterized using UV- Vis, DLS, HR-TEM and EDX. A well-defined NPs were obtained at high temperature (70 °C). The Au NPs had an average diameter of 92 nm at 25 °C and 66 nm at 70 °C. The zeta potential values were observed to be negative (-14 to -24) and indicate the stability of the Au NPs. The HR-TEM showed polydispersity, which decreased at higher temperature (70 °C). The stability of Au NPs in nutrient broth prior was conducted as well. All the Au NPs under study showed stability, only minimal changes in the UV-Vis spectra can be observed. Two plant extract viz Pistacia atlantica, Junipers phoenicea showed consistent results and forming stable and smaller NPs compared to others, both of the plant extracts and the corresponding NPs were tested against Streptococcus mutans and showed MIC value ~ 49 g/mL. In case of silver NPs, two plant extracts viz J. phoenicea, Rosmarinus officinalis, showed superior results than the others; both plants produced stable and small Ag NPs. The antibacterial activity against S. mutans demonstrated MIC valus ~ 50 g/mL. The synthesised NPs showed a promising bioactivity for developments of new antibacterial agents against S. mutans strains. Dose-dependent activity was observed for the tested NPs.