This study was conducted to determine whether nature-derivedReynoutria ellipticaextracts exhibit biocompatibility and antimicrobial effects against oral pathogens such asStreptococcus mutansandCandida albicans. Fine particles ofReynoutria ellipticaextract were used to probe for biocompatibility and antimicrobial activity toward these pathogens,and results were evaluated with an MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay, spectrophotometric growth inhibitory assay, the total number of colony-forming units (CFU), an agar disk diffusion test, and scanning electron microscopy (SEM). In addition, UV/VIS spectroscopy was used to determine the levels of flavonoid and polyphenol in experimental solutions. Several experimental groups showed cell viability higher than 70%, and the antimicrobial activity toward bothS. mutansandC. albicanswas significantly higher than was that seen for the control group. In CFU and agar disk diffusion tests withC. albicans, increases in the concentration ofReynoutria ellipticaextract led to significantly increased antimicrobial effects. Additionally, SEM results showed thatReynoutria ellipticaextract changed the morphology and density ofS. mutansandC. albicans. The results of this research can be applied to the use ofReynoutria ellipticaextracts for the development of oral products that are biologically friendly and can control oral diseases such as dental caries and candida-associated denture stomatitis.