| Spirulina is generally used as a nutraceutical feed supplement due to its nutrient profile, lack of toxicity, and therapeutic effects. This study aimed to explore the effect of dietary inclusion of Spirulina platensis (SPL) algae on growth, hemato-biochemical parameters, antioxidant status, and semen quality of cross-bred lambs (½ Finnish × ½ Ossime). Twenty-four lambs aged 10 months with 32.93±0.48 kg LBW were distributed into three groups (8/group). Lambs in G1 (controls) were fed a basal diet without treatment. In G2 and G3, the daily diet was supplied with 1 and 5 g SPL /kg from 10 to 15 months of age. Dietary SPL supplementation significantly increased body weight, count of red and white blood cells, packed cell volume, and serum total protein, high-density lipoproteins, testosterone, and thyroid hormones (T3 and T4), and significantly decreased activity of aspartate and alanine transaminases (AST and ALT), triglycerides, cholesterol, low-density lipoproteins (LDL), very-LDL, and urea. Semen variables including semen volume, and percentages of sperm motility, livability, and abnormality as well as concentration and output of sperm cells were significantly by SPL. In serum and seminal plasma, glutathione, superoxide dismutase, catalase, and glutathione peroxidase significantly increased, while malondialdehyde significantly decreased in SPL groups. Based on our results, spirulina as a dietary feed additive (5 g/kg diet) could be used safely for improving growth, health, antioxidant defense system, and semen quality of growing cross-bred ram lambs from 10 to 15 months of age.