Nanotechnology is being used effectively in many areas contemporarily. Silver nanoparticles (AgNPs) are one of the most crucial and remarkable nanomaterials involved in medical applications. These nanoparticles (NPs) have an important place in nanomedicine, nanotechnology, and in particularly, nanoscience. AgNPs are one of the most widely used materials in antibacterial and antiseptic practices. The synthesis of biogenic AgNPs has been applied as an alternative to physical and chemical synthesis. For this purpose, water extracts of Rhododendron ponticum were used for biosynthesis of AgNPs. Also, AgNPs were characterized by UV-vis spectrophotometer, scanning transmission electron microscope (STEM) and X-ray diffractometer (XRD). The antimicrobial activity of AgNPs synthesized with Rhododendron ponticum was analyzed by the Minimum Inhibition Concentration (MIC) test. Also, the biofilm inhibition test was made, and AgNPs showed a strong effect for biofilm inhibition. In addition, the prepared nanoparticles were tried for cytotoxicity activity with the help of MIT assay in MCF-7 and 4T1 cancer cell lines. (C) 2019 Elsevier B.V. All rights reserved.