Obesity is a major health problem worldwide that is associated with the increased risk of type 2 diabetes and other chronic diseases. Sasa veitchii, which belongs to the Gramineae family, has various properties including anti-obesity properties. However, detailed mechanism of anti-obesity was not reported. This study aimed to investigate the therapeutic effect of Sasa veitchii leaf extract (SE) on obesity characteristics induced by a high-fat diet (HFD) such as hyperglycemia, insulin resistance, and inflammatory response. Four-week-old male ddY mice were freely fed a HFD or a normal diet (control) for 12 weeks. During the experimental 12-week period, treatment with saline or SE, 0.2 mL twice per day by oral gavage, was conducted, and body weight was measured weekly. At the end of the experiment, the mice were euthanized after a 16-hr fasting period, and their plasma was collected. Liver and epididymal adipose tissue samples were collected and weighed. Moreover, after 10 weeks of feeding, oral glucose tolerance test was performed. Treatment with SE significantly decreased body weight, adipose tissue weight, plasma glucose, insulin, leptin, and pro-inflammatory cytokines compared with HFD groups, and markedly reduced the impairment of glucose tolerance in obese mice. Furthermore, HFD-induced adipocyte hypertrophy was improved by treatment with SE. Moreover, adipocyte differentiation marker such as proliferator-activated receptor γ was activated by SE treatment. Our findings demonstrate that SE may reduce obesity-induced glucose and insulin tolerance, presumably by the induction of the proliferator-activated receptor γ.