Hypoglycemic activity‐guided separation of ethanol extracts from the fruits of Cornus officinalis Sieb. et Zucc (CO) led to the isolation of loganin, morroniside, and ursolic acid. The antidiabetic capacity of CO extracts and related compounds was further investigated in diabetes mellitus mice. The results suggested that both CO extracts and pure compounds could ameliorate diabetes‐associated damages and complications. Oral administration of loganin and morroniside decreased fasting blood glucose levels in diabetes mellitus mice. Ursolic acid exhibited the highest reactive oxygen species scavenging activity and α‐glucosidase inhibitory activity. Notably, we noticed an interesting synergistic effect between loganin and ursolic acid. Given these favorable hypoglycemic properties, C. officinalis, a food and medicinal plant in China, may be used as a valuable food supplement for the treatment of diabetes mellitus. Copyright © 2015 John Wiley & Sons, Ltd.