¹Department of Biology, Duba University College, Tabuk University, Duba city, Tabuk, SAUDI ARABIA DOI : 10.9775/kvfd.2025.34339 The escalating threat of antibiotic resistance drives the search for alternatives, leading this study to investigate Spirulina platensis extract (SPE) as a substitute in broiler chicken feed. The research evaluated the impact of SPE on growth, antioxidant levels, blood profiles, and gut bacteria. SPE was found to contain antimicrobial organic active compounds, such as heptadecane and geosmin. A 420 broilers were divided into seven groups for a 35-day study: a control group, an Eimeria-infected group, and five SPE-supplemented groups. Of the supplemented groups, four received 0.5, 1, 2, or 3 mg/kg SPE, respectively, while one Eimeria-infected group also received 3 mg/kg SPE. Supplementation with 3 mg/kg SPE improved body structure, feed efficiency, weight gain, carcass quality, and gut pH. Liver enzymes and kidney markers were reduced. SPE lowered oxidative stress while maintaining antioxidant enzymes and improving gut microbiota and immunity. Eimeria infection in broiler chickens led to reduced growth performance, increased oxidative stress, and compromised immunity compared to the control group. However, the dietary inclusion of Spirulina platensis extract (SPE) at 3 mg/kg demonstrated a significant mitigating effect on these negative impacts in Eimeria-infected birds. Specifically, broilers infected with Eimeria and treated with SPE exhibited notable improvements in growth performance, reaching levels comparable to or surpassing those of non-infected chickens receiving SPE. Furthermore, SPE supplementation in infected birds effectively improved their antioxidant status, evidenced by reduced oxidative stress markers, and bolstered their immune response. These findings suggest that SPE possesses properties capable of counteracting the detrimental effects of Eimeria infection in broiler chickens, highlighting its potential as a supportive agent in managing coccidiosis and maintaining overall health and productivity in poultry. Keywords : Anticoccidial, Eimeria, Spirulina platensis, Gut microbiota, Immune response