In the previous screening on antidiabetic effect of Lycii fructus by glucose transport method using N₂-STZ diabeted rat model, each extracts showed the potent antidiabetic activity. We obtained three compounds isolated from the water fraction, EtOAc fraction and n-BuOH fraction of Lycii fructus in the present work and their structures were identified as 1-carboxy-N,N,N-trimethylmethanaminium hydroxide inner salt, 2,4(1H,3H)-pyrimidinedione and 3,3`,4`,5,7-pentahydroxyflavone-3-rutinoside. Among the constituents separated from Lycii fructus, 2,4(1H,3H)-pyrimidinedione, 3,3`,4`,5,7-pentahydroxyflavone-3-rutinoside and ascorbic acid were shown a remarkable antidiabetic effect.