This study was conducted to investigate the effect of dietary chromium and riboflavin supplementation on the performance, body composition, and serum cholesterol concentration of broiler under heat stress. A total of seventy-two 22d old male broilers Ross were assigned to 3 treatments ; control, chromium picolinate Sppm supplementation group(Cr group) and chromium picolinate 5ppm and riboflavin 10㎎/㎏supplementation group(CrRib group). During the 28 days of experimental period, all birds were housed in an environmentally controlled room and maintained at 34℃. Feed intake and body weight gain of CrRib group were higher (P$lt; 0.05) than those of the others at 42d. Feed conversion rates were not different among the treatments and began to decrease from 3wk. Relative weight of liver, breast muscle and leg muscle were not different, but abdominal fat weight was lower (P$lt; 0.05) in Cr group than in other groups. The serum cholesterol concentration of CrRib group was higher (P$lt;0.05) than that of the other groups. The result of this experiment suggests that supplementation of riboflavin improved broiler performance under heat stress and dietary chromium deceased abdominal fat weight.