Introduction: Microalgae are photosynthetic microorganisms that represent an excellent source of new natural products. The extracts of microalgae possess multiple therapeutic effects in humans and animals, including anticancer, antiviral, antioxidant, anti-inflammatory, and immunomodulatory activities. Aim: This study evaluated the impact of the microalgae Amphora coffeaeformis (A. coffeaeformis) on growth performance, hematological parameters, and immune function in immunosuppressive rats. Besides, the chemical composition, fatty acids (FA), phenolics, antioxidants, and polysaccharides constituents of A. coffeaeformis was identified. Methods: Gas chromatography-mass spectrophotometry was used to evaluate the chemical components (macro and micronutrients). The FA, total antioxidants, and total flavonoids were also assayed. The biological experiment was conducted on 50 male rats of which ten rats served as the control group. While the other 40 rats were immunosuppressed by injecting a single dose of sheep red blood cells. The immunosuppressed rats were divided into 4 groups (n=10), group 2 non treated immunosuppressive, and group 3, 4, and 5 A. coffeaeformis treated immunosuppressive (1, 2 and 3%, respectively). Results: The results of this study showed that A. coffeaeformis contains a high % of carbohydrates, proteins, metals, vitamins, phenols, antioxidants, polysaccharides, and polyunsaturated fatty acids (PUFA). Feeding the rats with A. coffeaeformis dose-dependently improved body weight gain (BWG%), feed intake (FI), feed efficiency ratio (FER), complete blood counts with, especially (RBCs, Hb, WBCs, LYMPH, and NEUT), and serum immunoglobulins (IgG, and IgM) compared to the immunosuppressed rats. Conclusion: Both the improved growth performance and immunity could be attributed to the bioactive ingredients of A. coffeaeformis.