Astaxanthin is known as a “marine carotenoid” and occurs in a wide variety of living organisms such as salmon, shrimp, crab, and red snapper. Astaxanthin antioxidant activity has been reported to be more than 100 times greater than that of vitamin E against lipid peroxidation and approximately 550 times more potent than that of vitamin E for singlet oxygen quenching. Astaxanthin doesn’t exhibit any pro-oxidant nature and its main site of action is on/in the cell membrane. To date, extensive important benefits suggested for human health include anti-inflammation, immunomodulation, anti-stress, LDL cholesterol oxidation suppression, enhanced skin health, improved semen quality, attenuation of common fatigue including eye fatigue, increased sports performance and endurance, limiting exercised-induced muscle damage, and the suppression of the development of lifestyle-related diseases such as obesity, atherosclerosis, diabetes, hyperlipidemia, and hypertension. Recently, there has been an explosive increase worldwide in both the research and demand for natural astaxanthin mainly extracted from the microalgae, Haematococcus pluvialis, in human health applications. Japanese clinicians are especially using the natural astaxanthin as add-on supplementation for patients who are unsatisfied with conventional medications or cannot take other medications due to serious symptoms. For example, in heart failure or overactive bladder patients, astaxanthin treatment enhances patient’s daily activity levels and QOL. Other ongoing clinical trials and case studies are examining chronic diseases such as non-alcoholic steatohepatitis, diabetes, diabetic nephropathy, and CVD, as well as infertility, atopic dermatitis, androgenetic alopecia, ulcerative colitis, and sarcopenia. In the near future, astaxanthin may secure a firm and signature position as medical food.