The present invention relates to N,N-dimethyl imidodicarbonimidic diamide acetate, a method of preparing the same and a pharmaceutical composition comprising the same, and more particularly, to N,N-dimethyl imidodicarbonimidic diamide acetate which is a crystalline acid addition salt prepared by reacting N,N-dimethyl imidodicarbonimidic diamide with acetic acid, and which is very effective as a therapeutic agent for treating metabolic syndromes that glycosuria and diabetes mellitus, obesity, hyperlipidemia, fatty liver, coronary heart disease, osteoporosis, polycystic ovarian syndrome, a cancer depleted of gene P53, etc. are complexly occurred; treating diabetes mellitus and preventing its complication; and treating a cancer and preventing myalgia, muscle cell cytotoxicity and rhabdomyolysis, etc. since the acid addition salt is excellent in physicochemical properties such as solubility, stability, non-hygroscopicity, anti-adhering property, etc., and low toxicity, a method of preparing the same and a pharmaceutical composition comprising the same.