This study investigated the anti-obesity properties of an extract of Geranium thunbergii (GTE) in high-fat diet-induced obese mice. GTE treatment significantly reduced body weight, adipose tissue mass, adipocyte size, as well as serum triglyceride, total cholesterol and low-density lipoprotein-cholesterol levels in obese mice compared to high-fat diet-fed mice. It also decreased serum leptin levels and increased adiponectin levels. The serum levels of aspartate transaminase, alanine transaminase, blood urea nitrogen and creatinine were not significantly changed in GTE-treated mice compared to serum levels in normal diet and high-fat diet-fed mice. Furthermore, GTE suppressed the mRNA levels of sterol regulatory element-binding protein 1c, peroxisome proliferator-activated receptor γ, adipocyte fatty acid-binding protein and fatty acid synthase in the adipose tissues of obese mice. These results suggest that GTE ameliorated high-fat diet-induced obesity by altering the adipokine levels and downregulating the expression of transcription factors and lipogenic enzymes involved in lipid metabolism.