Short-chain fructo-oligosaccharides (FOS) are known to have beneficial effects on health. However, the effects of FOS on insulin resistance have not been fully clarified. We observed the effects of FOS feeding on insulin sensitivity and adipocytokine release from abdominal adipocytes in weaning rats. Male Sprague–Dawley rats, 3 weeks old, were divided into three groups and fed a sucrose-based American Institute of Nutrition (AIN)-93 growth diet (control), the control diet containing 5 % FOS for 5 weeks (FOS-5wk) or the control diet for 2 weeks followed by the 5 % FOS diet for 3 weeks (FOS-3wk). Tail blood was collected after fasting for 9 h on day 33 of feeding, and glucose and insulin levels were measured. On the last day, rats were anaesthetised and killed after the collection of aortic blood. Small- and large-intestinal mesenteric fat tissues were immediately excised, and the release of adiponectin, leptin and TNF-α was evaluated from the subsequently isolated adipocytes. The weight of the large-intestinal mesenteric fat, fasting blood insulin level and homeostatic model assessment for insulin resistance decreased in a time-dependent manner, and were much lower in the FOS-5wk group than in the control group. These values were correlated with aortic blood leptin levels. The secretion rate of leptin from the isolated mesenteric adipocytes in the small intestine, but not in the large intestine, was lower in the FOS-fed groups than in the control group. In conclusion, FOS feeding improved insulin sensitivity accompanied by the reduction in large-intestinal fat mass and leptin secretion from the mesenteric adipocytes of the small intestine.