An experiment was designed to study the effects of a beta agonist, ractopamine, on body weight gain, feed intake, feed conversion ratio, carcass traits and blood biochemical parameters in male Japanese quail. Two hundred fifty six Japanese quail at the age of 14 d were randomly distributed to one of eight treatments which contained 0, 0.5, 1, 2.5, 5, 7.5, 10 and 20 ppm ractopamine in diet. The experiment lasted for four weeks. The average daily gain and feed conversion ratio and live body of the birds improved at the level of 7.5 ppm ractopamine. Carcass percentage, total protein and globulin increased significantly at the level of 7.5 ppm while blood cholesterol decreased (P<0.05) at the same level. From the results of this experiment, we concluded that dietary supplementation of ractopamine at 7.5 ppm in diet improved performance of Japanese quails.