in vitro, the sensitivity to different propolis extracts, at a concentration of 100 mg/ml, of staphylococcus aureus, staphylococcus sp. coagulase negative, streptococcus agalactiae and bacteria of the coliform group, isolated from the milk of cows with mastitis, was evaluated using the technique of an agar disk diffusion with a medium doublelayer. the results showed that the commercial propolis, the ethanolic extract, and, in a minor proportion, the methanolic extract inhibited the growth of the gram positive bacteria, staphylococcus aureus, staphylococcus sp. coagulase negative and streptococcus agalactiae. the extracts obtained through water, etila acetate and chloroform did not inhibit any bacterial strains, nor did the pure ethanol and methanol vehicles that were utilized as controls. the gram negative bacterium tested, from the coliform group, did not show sensitivity to any extract. bacterial strains of the same species collected from different sources presented significant differences in sensitivity to the extracts (p < 0.05). in the streptococcus agalactiae samples, the diameters of the zone of inhibition around the disks were bigger than those observed for samples of staphylococcus aureus and staphylococcus sp. coagulase negative. the results of this experiment stimulate the continuation of studies on the use of propolis extracts, by means of using the appropriate vehicles for the treatment of bovine mastitis.