This study focused on a prominent haemagglutination feature of the pathogenic M. gallisepticum, which have agglutinins that are immunogenic surface protein. M9 protein was prepared using cloning and expression technology and evaluated as haemagglutinating antigen. In comparing its haemagglutination properties with the whole cell antigen, the M9 protein showed somewhat less sensitivity starting after the first week post infection with M. gallisepticum strains and reaching the maximum reactivity at the seventh week post infection, while the whole cell antigen reached its maximum reactivity at the sixth week post infection. Regarding the specificity, both antigens are highly specific and showed no reactions with the M. synoviae antisera. The advantages of M9 protein as haemagglutinating antigen is that it could be used in different areas and is cheaper in preparation.