PURPOSE: A composition containing poly gamma glutamic acid for preventing and treating obesity is provided to suppress differentiation of adipocytes and to activate AMPK(5'AMP-activated protein kinase). CONSTITUTION: A composition for preventing and treating obesity contains poly gamma glutamic acid(PGA) as an active ingredient. The molecular weight of PGA is 100kDa to 15,000kDa. The composition is a pharmaceutical composition or food additive. The composition further contains pharmacologically acceptable carrier. The composition is manufactured in the form of powder, granules, tablets, capsules, suspension, emulsion, syrup, external use, suppository, or sterilized injection solution.본 발명은 폴리감마글루탐산을 유효성분으로 함유하는 비만예방 및 치료용 조성물을 제공한다. 본 발명에 따른 비만예방 및 치료용 조성물은 약제학적 또는 식품조성물로서 지방세포의 분화를 억제하여 비만예방 및 치료에 탁월한 효과를 발휘한다.