The aim of this study was to investigate the therapeutic effect of Sasa veitchii leaf extract (SE) on features of obesity induced by a high-fat diet (HFD), such as hyperglycemia, insulin resistance, and inflammatory response. Four-week-old male ddY mice were freely fed HFD or control normal diet for 12 weeks; half was given SE in addition twice per day in weeks 8-12. Glucose and insulin intolerance were estimated, and body weight measured, weekly throughout the study. Following the experiment, the mice were fasted for 16 h, euthanized, and plasma was collected. Liver and epididymal adipose tissue was collected and weighed. Treatment with SE significantly decreased body weight, adipose tissue weight, plasma glucose, insulin, leptin, and tumor necrosis factor α compared with HFD groups, and markedly reduced the impairment of glucose and insulin tolerance in obese mice. Furthermore, hepatic steatosis and hepatic insulin receptor substrate were improved by treatment with SE. Our findings demonstrate that SE may reduce obesity-induced glucose and insulin tolerance, not only by suppressing inflammatory responses but also by improving insulin signaling.