In this report, in vitro antibacterial activities of 3 antimicrobial agenst against the five mycoplasmal soecies were determined by using the broth dilution and an agar dilution methods. The results indicated that Jasamycin and tylosin are highly active against the five mycoplasmal species Jasamycin is equally active against Uu、Mh、M、orale (MIC50 to MIC90,0.0625 to 0. 125μg/ml), whereas the MIC50 to MIC90 for M. Salivurium and M. arginini are 0. 125 to 0. 25μg/ml. Tylosin is active against Uu and Mh, with a MIC50 to MIC90 of 0. 5 to 1μg/ml...