To evaluate the effect of feeding level and dietary supplementation of dried Baker's yeast (DBY) on the performanceof Friesian growing calves, total of 36 calves with average body weight of 160±2.34 kg and 9.47±0.30 mo of age were assigned randomly into three feeding level groups 80, 100 and 120% of NRC (1989), 12 animals in each. Each feeding level group was further divided into two equal subgroups, one without dietary supplementation (control) and another group supplemented with 10 g DBY/h/d. 6 animals in each. Feeding level lasted for ????. Results show during the summer or winter feeding, calves fed 80% with DBY showed the highest (P<0.05) digestibility coefficients for most nutrients, while the lowest values were almost obtained for those fed 120% without DBY diet. Live body weight (LBW) of calves was the highest (P<0.05) with 120% feeding level plus DBY, while the lowest LBW were recorded with 80% without DBY. Average daily gain (ADG) increased (P<0.05) by increasing feeding level from 100 to 120%. However, DBY supplementation improved (P<0.05) ADG only with feeding level of 80%. The best feed efficiency was recorded (P<0.05) for calves fed 80% with DBY, while those fed 80 or 100% without DBY showed the poorest (P<0.05) feed efficiency. Feeding level showed marked (P<0.05) effect on pH values, and concentrations of total volatile fatty acids (TVFA) and NH₃-N in RL during summer and winter feeding. However, the effect of DBY supplementation was more pronounced (P<0.05) TVFA concentrations in RL during summer and winter feeding. Total protein and globulin concentrations in blood plasma increased (P<0.05) by increasing feeding level. However, DBY supplementation increased (P<0.05) total protein concentration only with 80% feeding level. Overall concentration of T4 in blood plasma increased (P<0.05) feeding level up to 120%, and was not affected by DBY supplementation. According to this study growing Friesian calves fed 80% with DBY showed the highest feed efficiency from the nutritional and economical points of view.