Dental caries is an infectious disease of worldwide public health concern. Among the bacteria involved in this pathology are Streptococcus mutans, Streptococcus sobrinus and organisms belonging to the genera Actinomyces and Lactobacillus. The pharmaceutical industry is focussing on the discovery of new antibacterial products after a greater resistance to those already known. Propolis has been used since ancient times, so their effects against various microorganisms have been already investigated. In our study, we evaluated the antimicrobial effect of 6 commercial ethanolic propolis extracts on the bacterium Lactobacillus fermentum. This bacterium was isolated after its identification by Polymerase Chain Reaction using species specific primers, and after growing microbiological samples from cavities of patients diagnosed with dental caries and with indication of tooth extraction. L. fermentum was detected in 9 of 40 patients, corresponding to 22%. The susceptibility study, carried out by microplate dilution, found antimicrobial activity in four of the six ethanolic extract of propolis used. These differ in the effective concentration against the microorganism, which can be attributed to factors such as the botanical origin, geographic location and harvest season. Among the results, it was noticed that these polyphenols showed concentrations ranging between 9 ± 0.3 and 85 ± 2.1 mg/mL. The chromatographic analysis allowed the identification of caffeic acid, myricetin, quercetin, kaempherol, apigenin, pinocembrin, galangin and caffeic acid phenethyl ester (CAPE). Our study demonstrates the antimicrobial action of propolis on L. fermentum, the patogen related to caries development.