To evaluatethe effects of supplementing diets of growing Japanese quails (n=450; 7 days old) with chromium (Cr) yeast and / or MANNAN oligosaccharides (MOS) on productive performance, carcass traits and the immune system are reported. Diets were a basal diet (control) or the basal diet supplemented with 600 mg Cr-yeast/kg (Cr 1), 1200 mg Cr-yeast/kg (Cr 2), 1.0 g MOS/kg, Cr 1+MOS or Cr 2+MOS. Quails fed Cr 1, MOS or Cr 1+MOS diets had similar final live body weight and weight gain, with both groups being higher than the control. Feed conversion tended to be improved with dietary supplements. Carcass traits did not differ among treatments. Primary and secondary humoral immune responses of quails fed the supplemented diets were higher than the control. Plasma total proteins and triiodothyronine were increased, while plasma total lipids and cholesterol were decreased by the supplements. In conclusion, dietary supplementation with Cr yeast (600 mg/kg) and / or MANNAN oligosaccharides (1.0 g) improved productive performance and immunity and reduced total cholesterol of growing Japanese quails.