The activated immune systems with lipopolysaccharide(LPS) were evaluates by ${gamma}$- globulin levels in domestic cats. Especially, cats were in a stress condition, which was unfamiliar environmental change. Effect of continuous unfamiliar environmental stressor was a diminution of production of serum total globulin auld ${gamma}$- globulin on feline infectious peritonitis(FIP) vaccination. The ${gamma}$-globulin production on FIP vaccination more increased in LPS treated 77ups than non-LPS treated group. Also. the ${gamma}$-globulin production on FIP vaccination was maintained in LPS treated group under stress condition. These results imply that that the ${gamma}$-globulin can be produced under a stress condition by mitogen like as LPS.