The study in the reducing in postprandial glycemia of Cleistocalyx operculatus (Roxb.) Merr and Perry flower bud in 20 type 2 diabetic patients was carried out in Hanoi. There are 2 days to do the experiments: the first day, patients were given 150 ml of water with eating the meal (330 kcal); the second day (after the first day is 7 days), all these 20 patient were given 150 ml of Nu Voi tea and eating the same meal. The blood glucose levels were determined at initial time and at 15, 30, 60 and 120 min after eating. Results, increase of the postprandial blood glucose level of subjects in the nu voi tea day was significantly lower than that in control day. Significant differences of blood glucose increments at 30 min was established between the water day and the nu voi tea day (10,67 and 11,92 mmol/L; p<0,05). The difference of blood glucose AUCs between each meal with and without nu voi tea was statistically significant (23,89 vs. 25,66 mmol/L.hr; p<0,01). The results of study suggested that nu voi can be a potential material supporting to control the post prandial blood glucose level in diabetic patients. And, nu voi tea can be used as a beverage for preventing diabet.