ABSTRACT Background: Nanoparticles (NPs), such as green cobalt NPs (CoNPs), are easier to pass through cell membranes in animals and interact rapidly with biological systems. Therefore, using green CoNPs is one of the recommendations for enhancing the bioavailability of cobalt, thereby improving its absorption. Objectives: The goal of this study was to explore the influences of biological nano-cobalt (BNCo) as a feed supplement on broiler growth performance, haematology, blood chemistry, antioxidant activities, immunological status, digestive enzymes and carcass characteristics. Methods: A total of 300 Arbour Acre broiler chicks, all unsexed, were distributed into 5 treatment groups, each containing 60 chicks, at random. Five replications of each group were formed, each containing 12 chicks. The first group received a control diet free of BNCo, whereas the second, third, fourth and fifth groups were administered diets fortified with BNCo at concentrations of 100, 200, 300 and 400 ppm, respectively. Results: The results illustrated a significant increase in body weight (p < 0.001), body weight gain (p < 0.001) and improvement in feed conversion ratio (p < 0.01) in comparison to the control diet. BNCo supplementation significantly increased the percentage of immune organs, especially the spleen and thymus (p < 0.05, p < 0.01). Moreover, BNCo supplementation significantly increased haemoglobin (Hb) (p < 0.01), red blood cells (RBCs) (p < 0.05) and white blood cells (WBCs) (p < 0.05). In broiler chickens, BNCo supplementation increased serum levels of total protein, albumin and globulin significantly (p < 0.05) and reduced serum levels of aspartate aminotransferase (AST) activity (p < 0.001) and alanine aminotransaminase (ALT) (p < 0.01). The BNCo in feed supplementation raised blood levels of cobalt and markedly improved lipid markers, immunological and antioxidant status (p < 0.05). Furthermore, digestive enzymes were significantly boosted (p < 0.05) by BNCo treatments. Conclusion: The results indicated that BNCo supplementation at 200 ppm/kg diet produced the best overall performance, demonstrating its potential as an innovative additive for broiler diets.