Lysozyme (LZ) concentration, in human and animal species milk, is very different; its antibacterial activity is directed against certain bacterial species. The aim of the present work is to evaluate the antibacterial activity of 3 different donkey milk (DM) bulk samples, on a total of 43 bacterial strains isolated from donkey and bovine milk. The activity was determined by Kirby Bauer (KB) method and by microtiter plates method; MIC was calculated. Bacterial strains showed no susceptibility with KB method. Vice versa, with microtiter plates, milk sample n.1 inhibited only 1 Pseudomonas spp strain (MIC: 5800 U/ml); sample n.2 (MIC:2740 U/ml) never had antibacterial effect; sample n.3 (MIC:3400 U/ml) prevented a 50% of Staphylococcus aureus strains from DM. LZ showed no activity against the bovine milk strains. Finally, the authors underline that a better assessment of LZ antimicrobial activity would be advisable, both for some veterinary health purposes and for consumer (infants with some milk proteins intolerance) security.