**Abstract**

Marine seaweeds are a promising source of bioactive secondary metabolites that can be utilized in drug development and nutraceuticals. Diabetes mellitus is a leading non-communicable disease, and it is the third leading cause of death worldwide. Among the types of diabetes, type 2 became the major health problem as it is associated with severe health complications. Since available oral hypoglycemic drugs cause several adverse effects, it is worth searching for a natural cure with fewer or no side effects that may benefit patients with type 2 diabetes. Among the marine seaweeds, brown and red seaweeds are extensively studied for the anti-diabetic activity compared to the green seaweeds. Bioactive compounds present in marine seaweeds possess anti-diabetic potential through diverse mechanisms, mainly by reducing postprandial hyperglycemia and associated complication. Most of the studies emphasized that the marine seaweeds control the hyperglycemic condition by inhibiting carbohydrate hydrolyzing α-amylase,α glucosidase enzymes, and the inhibitory effect of dipeptide peptidase-4 that are involved in the degradation of incretins. Similarly, bioactive compounds in marine seaweeds can reduce diabetes complications by inhibiting angiotensin-converting enzymes, aldose reductase, protein tyrosine phosphatase 1B enzyme. This chapter focuses on the anti-diabetic potential of marine brown, green, and red seaweeds through different mechanisms.

**Keywords:** Marine seaweeds, microalgae, bioactive compound, diabetes, drug discovery, mechanisms of action
