Type 2 diabetes mellitus (T2DM) is a life-threatening metabolic disorder that possibly leads to serious health conditions. T2DM is characterized by hyperglycemia and hyperlipidemia. Despite their side effects, synthetic drugs remain the core concept of treatment of type-2 DM. However, natural ingredients e.g., fucoidans were investigated to possibly alleviate the symptoms of DM with minor adverse effects. Owing to their structural complexity, fucoidans exhibit a broad range of therapeutic activities such as anti-hyperglycemic and antioxidant potentials. The present book chapter exclusively focuses attention on the potential therapeutic effect of fucoidan on hyperglycaemia and diabetic complications resulting from uncontrolled lifestyle. We concluded that fucoidan is a crucial source of marine seaweeds as well as protective non-toxic compounds in alleviating the symptoms and complications of T2DM.