Aim To investigate the effeet of dihydro- myricetin ( DHM ) on cognitive dysfunction in type 2 diabetes mellitus ( T2DM) rats and its mechanism.Methods SD rats were randomly divided into the normal control group ( n = 56) : normal diet and citrate buffer solution (30 mg • kg 1 ) ; T2DM model group (n =60) : high glucose, fat and low dose STZ ( 30 mg • kg 1 ) ( Four unsuccessful rats were eliminated ).Then rats in the above two groups were treated with or without DHM (250 mg • kg 1 • d intragastric).After 12 weeks, eight rats in each group were randomly selected to perform Morris water maze and Y maze test to observe the effect of DHM on cognitive function of rats.The remaining rats in each group were injected ERS antagonist tauroursodeoxycholic acid ( TUDCA ) 10 jxg • d 1 or ERS activator tunicamycin (TUN) 10 jxL, respectively.After the behavioral analysis, the hippocampal tissues of rats were taken out.The expressions of EH stress related proteins GRP78 and P- PERK were detected by Western blot.Results Both DHM and TUDCA could improve cognitive dysfunction in T2DM rats.On the contrary, TIJN reduced the effect of DHM on cognitive dysfunction in T2DM rats.TUDCA decreased the expression of GRP78 and p- PERK proteins in T2DM rats, while TUN increased the expression of GRP78 and p-PERK proteins in T2DM rats treated by DHM.Conclusion DHM improves cognitive dysfunction in T2DM rats, and the mechanism may be related to the inhibition of endoplasmic reticulum stress.