Stryphnodendron adstringens (Mart.) Coville is a medicinal plant known for its anti-inflammatory and antimicrobial properties. This study evaluated some biological activities of extract from S. adstringens. Antimicrobial activity was checked in planktonic cultures and monomicrobial biofilms on aerobic, and anaerobic dental microorganisms. Analyzes of cytotoxicity using MTT assay, and genotoxicity by micronucleus test were performed in human keratinocytes (HACAT), murine macrophages (RAW 264.7), and murine fibroblasts (L929). The anti-inflammatory effect was checked in RAW 264.7 stimulated by lipopolysaccharide (LPS) from Escherichia coli, and treated with the plant extract. The levels of cytokines, and nitric oxide (NO) were measured by ELISA, and Griess method, respectively. Data were analyzed by ANOVA, followed by Tukey's, or Kruskal-Wallis, and Dunns tests (P ≤ 0.05). Biofilms of anaerobic bacteria were very susceptible to the plant extract. Effective concentrations showed cell viability > 50%, except 25 mg/mL for HACAT after 24 h of exposure. The extract of S. adstringens was not genotoxic for RAW 264.7. LPS associated with extract increased the production of all cytokines, except TNF-α. However, the plant extract decreased the production of NO. In conclusion, the extract of S. adstringens affected biofilm of anaerobic bacteria using non-cytotoxic concentrations for RAW 264.7, L929, and HACAT cells.