Objective: To determine the antibacterial, in vitro activity of ethanolic extract of Caesalpinia spinosa (Tara), on the oral biofilm bacteria cultures. Material and methods: An in vitro experimental study was carried out, in which the antibacterial activity of an ethanolic extract of C. spinosa and the controls (chlorhexidine 0.12%, oral antiseptic (OA), ethanol and distilled water), were compared to strain cultures strains of Streptococcus mutans (ATCC® 25175), Streptococcus sanguinis (ATCC® 10556), Enterococcus faecalis (ATCC® 29212), Staphylococcus aureus (ATCC® 6538) and Porphyromonas gingivalis (ATCC® 30277). The agar diffusion method with 6 mm diameter wells was used, with the experimental group and controls Results: It was evident that the average of the inhibition zone formed by the application of the ethanolic extract of C. spinosa on S. aureus was much larger than the one ...