The azuki bean (Vigna angularis) has been one of the most important and traditional crops of East Asia, where it has long been cultivated. In Japan, the azuki bean is the second-most important legume after soybeans, and it is commonly used as an essential ingredient, e.g., seki-han, a festive rice dish and an, a sweetened bean paste. Azuki beans (V. angularis) have been known to contain proanthocyanidins, a group of polyphenolic bioflavonoids with remarkable radical-scavenging activities. However, little research has provided detailed discussion of the beneficial effects and physiological functions of azuki beans involved in human body. Based on our findings, the authors provide here evidence that azuki bean (V. angularis) extract — including the molecules therein, such as proanthocyanidins and/or dietary fibers — may play a role in suppressing increases of oxidative stress and macrophage infiltration in the kidneys of animal models with hypertension and hyperglycemia. Moreover, azuki bean (V. angularis) extract may affect the vascular and renal expressions of endothelial nitric oxide synthase, which contribute to nitric oxide production. This review aims to summarize findings concerning the beneficial and interesting effects of azuki beans, especially the physiological functions of azuki bean (V. angularis) extract in treating inflammation, hypertension, and diabetic nephropathy.