Background and Objectives: This randomized, placebo-controlled trial was performed for 8 weeks to investigate the potential effects of astaxanthin (AST) supplementation on the adiponectin concentration, lipid peroxidation, glycemic control, insulin sensitivity, and anthropometric indices in participants with type 2 diabetes mellitus. Methods and Study Design: We enrolled 44 participants with type 2 diabetes who met our inclusion criteria. Eight milligrams of AST supplementation or a placebo were randomly administered once daily for 8 weeks to these participants. Results: The 8-week administration of AST supplementation increased the serum adiponectin concentration and reduced visceral body fat mass (p＜0.01), serum triglyceride and very-low-density lipoprotein cholesterol concentrations, and systolic blood pressure (p＜0.05). Furthermore, AST significantly reduced the fructosamine concentration (p＜0.05) and marginally reduced the plasma glucose concentration (p=0.057). Conclusions: We demonstrated that because participants with type 2 diabetes often have hypertriglycemia and uncontrolled glucose metabolism; our findings of dual beneficial effects are clinically valuable. Our results may provide a novel complementary treatment with potential impacts on diabetic complications without adverse effects.