The present invention relates to an adjuvant composition containing poly-gamma-glutamic acid-chitosan nanoparticles and a vaccine composition containing the adjuvant composition, and more particularly to an adjuvant composition containing nanoparticles prepared by ionic bonding between poly-gamma-glutamic acid having ensured safety and chitosan, and a vaccine composition containing the poly-gamma-glutamic acid-chitosan nanoparticles and an antigen. The adjuvant containing the poly-gamma-glutamic acid-chitosan nanoparticles has little or no toxicity and side effects and is added to human or animal vaccines for the prevention and treatment of viral and bacterial infections and cancers to increase the production of antibodies.