¹Department of Biology, Faculty of Science, Taibah University, Madinah, SAUDI ARABIA DOI : 10.9775/kvfd.2025.34198 The rise of antibiotic-resistant microbes has prompted a search for effective alternatives to antibiotics. This study evaluated the effects of Spirulina platensis extract (SPE) as a dietary supplement and a potential alternative to antibiotics for broiler chickens, focusing on growth performance, antioxidant activity, blood parameters, and cecal microbiota. SPE contained antimicrobial active compounds, including heptadecane and geosmin. A total of 300 broilers were divided into five groups (T1-T5). T1 received a basal diet (control), while T2-T5 were supplemented with 0.5, 1, 2, and 3 mg SPE/kg of diet, respectively, for 35 days. Results showed that including SPE (3 mg/kg) in the broiler diet significantly enhanced growth, decreased the feed conversion ratio (FCR), and improved body weight gain (BWG, 9%), while maintaining optimal carcass quality and intestinal pH at 6.8. Liver enzymes remained stable, with a 13-45% reduction in kidney markers based on the SPE concentration. SPE (3 mg/kg) also reduced oxidative stress by decreasing malondialdehyde (MDA) levels while sustaining antioxidant enzyme levels. The cecal microbiota showed an increase in lactic acid bacteria and exhibited enhanced immunity compared to the control. Additionally, SPE improved meat quality by boosting protein and moisture content, enhancing juiciness and tenderness. In conclusion, supplementing broiler diets with SPE (3 mg/kg) enhances growth performance, productivity, overall health, and disease resistance, making it a potential viable alternative to antibiotics. Keywords : Eco-friendly antibiotic, Broiler chickens, Spirulina platensis, Immune response, Gut microbiota