The growth performance, biochemical parameters, antioxidant status and thyroid hormones of growing heat-stressed calves fed on a diet containing Moringa oleifera leaves powder (MOLP) as a natural antioxidant were assessed in this study. Fifteen calves aged eight months and weighing 130-136 kg were randomly distributed into three treated groups with five calves each. The control group (M0) fed concentrate mixture without any supplement and the treated groups M1 and M2 fed concentrate mixture with 0.3% and 3.0% MOLP supplementation, respectively. The results demonstrated that MOLP supplementation significantly improved (P≤0.01) the final body weight, total weight gain, and average daily gain in both M1 and M2 groups recording the highest values in M2. MOLP supplementation considerably (P≤0.01) reduced serum total cholesterol, triglycerides, low-density lipoproteins and malondialdehyde concentration recording lower values in M1 group, while improved (P≤0.01) serum total antioxidant capacity and catalase activity where the greatest levels were recorded in M1. Conversely, serum concentrations of high-density lipoproteins, total protein, globulin, thyroxin and superoxide dismutase activity were non-significantly elevated in both supplemented groups. Serum glucose and triiodothyronine concentrations were increased significantly (P≤ 0.01) in M1 however, serum albumin and urea concentrations were significantly increased (P≤ 0.01) only in M2. Serum alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase activities and creatinine concentration were significantly decreased (P≤ 0.01) in the supplemented groups however, glutathione peroxidase activity was significantly increased (P≤ 0.01) in both groups. Therefore, dietary MOLP supplementation can be used to improve growth, biochemical and antioxidant parameters in heat-stressed calves without any adverse effects.