Chronic respiratory disease (CRD) caused by Mycoplasma gallisepticum (MG) can be prevented by using vaccine. This. article presents the study of clinical efficacy of F Vax-MG vaccine (Intervet), a live vaccine using in chicken of 6 week old, on the commercial layers of Babcock Brown breed. The results showed that the vaccination did not disturb the flock in the aspect of general health or respiratory signs. Antibody against MG was detected from 100 percent blood samples at six weeks after vaccination day. Average body weight was 1480.4g at 18 week old. Egg production was 66.81 percent at 23 weeks old and average egg weight was 55.3g. There was no specific lesion of MG found from dead chicken. Therefore, F Vax-MG is safe vaccine, stimulates the immunity and maintains good production for layers chicken.