The effect of prolonged vinegar feeding on postprandial blood glucose response was examined in totally gastrectomized and untreated rats. A basal diet and a vinegar diet were used for this experiment. The vinegar diet was prepared by the addition of powdered vinegar to the basal diet at a level of 7% (about 1% as acetic acid). The animals were fed with the basal or the vinegar diet for 10 weeks, and then orally administered 250mg of glucose per 100 g body weight as 20% glucose solution. Among untreated rats, the postprandial blood glucose level was significantly lower in rats fed the vinegar diet than in those fed the basal diet. On the other hand, prolonged feeding with the vinegar diet produced no effects in the totally gastrectomized rats. These results suggest that prolonged feeding with vinegar changes the postprandial blood glucose response by delaying the gastric emptying rate.