Japanese barnyard millet is gaining popularity in Japan. However, the utilization of bran is limited. Additionally, the role of Japanese barnyard millet bran in regulating glucose metabolism has not been fully investigated. In this study, we investigated changes in blood glucose levels in normal rats, as well as its ameliorative effects in streptozotocin-induced diabetic rats. The increase in blood glucose levels was lower in rats fed the bran diet than in those fed the control diet. In diabetic rats, a bran diet reduced diabetic polyuria, water intake, and HbA1c levels. The expression of heme oxygenase-1, an antioxidative enzyme, was higher in the liver of diabetic rats fed a bran diet. These results suggest that bran reduces the acute increase in blood glucose levels post feeding and has ameliorative and antioxidative effects in diabetic conditions. Thus, Japanese barnyard millet bran may be used a potential food material for maintaining glucose metabolism.