This study was conducted to investigate the effect of partial replacement of the crud protein of the concentrated feed mixture by Moringa oleifera leaves (MOL) on growth performance, hematological profile, and some blood plasma constituents of growing lambs. Twenty-four healthy male Farafra lambs (5 and 6 months old and 30 ± 0.50 kg body weight) were randomly divided into four groups. The first group was fed on 60% of the concentrated feed mixture (CFM) and 40% wheat straw as DM and served as a control. The other 3 treatment groups (10 MOL, 20 MOL, and 30 MOL), partially substituted the crud protein of the CFM at rates 10, 20, and 30% with Moringa oleifera leaves protein, respectively. The results revealed that dietary MOL had no significant effect on body weight gain, however they may adversely be affected by increasing the levels of MOL.  The inclusion MOL at 20% in the diet of lambs increased (P <0.05) WBC's count particularly neutrophils as compared with other groups. Also, MOL groups tended to be higher in RBC's count and percentages of HG and HCT than control one. The plasma albumin was decreased (P˂0.05) with increasing levels of MOL in the diets of lambs. Also, the urea concentration and ALT values were lower (P˂0.05) with MOL supplementation at Levels of 20 and 30% than that in 10% group.  It could be concluded that the partial substitution of concentrate feed with Moringa oleifera leaves up to 10 % growing lambs' diets can improve growth performance, blood hematology, and plasma constituents, and exert protective effects in the liver without inducing adverse effects on animal health.