Euterpe oleracea (Açaí) fruit are widely consumed at the Brazilian Amazon region, and biological potentials such as immunomodulatory and antioxidant have been described for its extracts. However, its antimicrobial properties remain poorly investigated. Here, the antimicrobial and antibiofilm activities of the methanolic extract of an artisanally-manufactured açaí pulp (MEAP) were evaluated against clinical isolates of Staphylococcus aureus. Besides, MEAP interference on the activity of antimicrobial drugs of clinical relevance was explored, and its cytotoxicity against hepatocellular carcinoma cells (HepG2) was investigated. Biochemical and physicochemical properties of the pulp were investigated, and the presence of polyphenols on the extract was confirmed. For the first time, we report that the methanolic extract of açaí pulp is effective against planktonic cells and biofilms of S. aureus, and also decreased the proliferation of HepG2 cells. Statistically significant synergism was observed when the extract was combined to the tested antimicrobials except for erythromycin, and all biochemical and physicochemical parameters ranged within the accepted values established by the Brazilian legislation. Our data open doors for more studies on the antimicrobial activity of phytomolecules isolated from Euterpe oleracea extracts, and also for its combined use with antimicrobial drugs.