This study was carried out to assess Melissa officinalis (MO) effects on the growth performance, hematological parameters, blood biochemical, antioxidant indices, and ruminal fluid contents of growing Ossimi lambs. Lambs (n=21) were randomly assigned to three similar groups (7 each). The first group (T1) was fed the basal diet without any supplementation and served as control. The other groups were fed the basal diet supplemented with MO at a level of 8g/kg DM (T2) and 12g/kg DM (T3). MO supplementation with 8 and 12g/kg DM improved (P < 0.05) body weight (10.27 and 13.31%), weight gain (25.51 and 32.46%), and feed conversion (10.76 and 13.92%) compared to the control group, respectively. The treated groups outperformed the control group, in terms of feeding values and digestibility coefficients. Erythrocyte count was significantly (P < 0.05) higher in T2 and T3 than in the control (T1), while leukocyte count was not affected (P> 0.05). Concentration of serum total-cholesterol, triglycerides, creatinine, and urea as well as activity of aspartate transaminase were reduced (P<0.05) by MO (12g/kg DM) compared with control diet. Moreover, catalase and superoxide dismutase activities were numerically higher (P<0.05) by 5.36 and 15.29% in T3 than in the control group, respectively. Meanwhile, level of malondialdehyde content was lower (P< 0.05) in T2 and T3 (33.80 and 40.38%) than in T1, respectively. Ruminal content of total nitrogen and ammonia decreased (P<0.05), but bacterial and protozoa counts were increased (P< 0.05) in T3 compared to the control group (T1). In conclusion, Melissa officinalis supplementation enhanced growth performance, lipid profile, antioxidant lipid peroxidation, antioxidant enzyme activity, and ruminal liquor parameters of growing lambs. Therefore, it may be used as a growth promoter or as a natural antioxidant for growing lambs.