Obesity, which is characterized by excessive body fat accumulation and energy imbalance, is a major risk factor for type 2 diabetes mellitus. Boesenbergia rotunda rhizomes (known as fingerroots) exhibit a variety of pharmacological activities and are used in traditional medicine. Pinostrobin was identified as a major constituent of Boesenbergia rotunda rhizome (BR) extract and suppressed nitric oxide production in interleukin 1β-treated hepatocytes. Next, we investigated the anti-obesity effects of BR extract in ob/ob mice, a type 2 diabetes mellitus model. The ob/ob mice were treated with or without 1% BR extract for 14 days and then analyzed for serum insulin and triglyceride levels, liver histology, and liver mRNA expression. The administration of BR extract significantly decreased blood glucose concentrations and increased serum insulin concentrations in ob/ob mice. In addition, this treatment reduced triglyceride levels in both the serum and liver and decreased lipid accumulation in hepatocytes. Microarray analysis revealed that hepatic mRNA affected the expression of genes involved in inflammation, lipid metabolism, lipid synthesis, and insulin signaling, leading to improvements in obesity. Because BR extract has hypoglycemic and antidiabetic effects on ob/ob mice, it might be a promising candidate for addressing obesity and related metabolic disorders.