A safe, economical, and convenient food drink having the effect of treating, preventing, or improving diabetes or diabetic complications without involving significantly changed dietary life habits is provided. A food or drink is provided for treating, preventing, or improving diabetes or diabetic complications, comprising oligosaccharides at a concentration of 0.15 to 10% by weight wherein the oligosaccarides include mannose molecules linked together with degree of polymerization of 2 to 10 (inclusive).