Provided is a composition for preventing, improving or treating obesity, which includes a Platycodon grandiflorum extract as an active ingredient and a method for preparing the extract with an improved anti-obesity effect. The extract shows an effect of inhibiting increases in body weight and fat mass caused by a high-fat diet for normalization, an increase in fasting blood glucose and a decrease in energy expenditure in a diet-induced obesity mouse model. Further, compared to an extract prepared by a conventional extraction method, the Platycodon grandiflorum extract shows a more excellent effect of inhibiting increases in body weight and fat mass, fasting blood glucose, and blood lipid and adipokine contents in experiments, resulting in an excellent anti-obesity effect. Therefore, the Platycodon grandiflorum extract prepared is expected to be useful for preventing obesity and treating obesity-related complications that can be caused by an increase in fat mass as well as obesity.
