Abstract: Diabetes mellitus (DM) is a condition in which the regulation of homeostasis of carbohydrate and lipid metabolism by insulin is improper. This research paper was designed to explore how brown algae (Sargassum subrepandum) powder (BAP) affect DM and its complications (hyperlipidemia and immune disturbances) that alloxan induces in rats. Thirty-six rats were distributed to two groups: (Group 1, 6 rats) received basal diet (BD) and the other (30 rats) received alloxan then distributed to five subgroups: group (2) received BD as a model control, and the four remaining groups received BD with 2.5, 5.0, 7.5 and 10 % BAP. By completing the trial (4 weeks), treatment of rats with alloxan, model control group, induced a significant (p≤0.01) rise in the concentration of serum glucose by 165.38% compared with the control group. Dietary intervention with BAP (2.5, 5.0, 7.5 and 10%) in rats for twenty-eight days resulted in a significant (p≤0.05) decline in serum glucose levels, recording 155.71, 137.08, 108.64 and 91.14% compared with the control group. The decrease rate in serum glucose was presented as a dose-dependent increase with the levels of BAP intervention. Also, BAE was effective in protecting against DM complications including serum lipid profile (TG, TC, HDL-c, LDL-c and VLDL-c) and serum immunological parameters (Alb and TNF-α). Thus, the study recommends using the powder of this alga to 10% in food, beverages, as well as dietary supplements.