Disclosed herein are a novel dicarboxylic acid salt of N,N-dimethylimidodicarbonimidic diamide, a preparation method thereof and a pharmaceutical composition comprising the same. More specifically, disclosed herein are a novel dicarboxylic acid salt of N,N-dimethylimidodicarbonimidic diamide, a crystalline acid addition salt prepared by allowing N,N-dimethylimidodicarbonimidic diamide to react with a specific dicarboxylic acid, which has improved physical and chemical properties including solubility, stability, non-hygroscopicity and anti-adhesive properties, and low toxicity, and thus is very effective in the prevention and treatment of not only diabetes and its complications in patients with so-called metabolic syndromes, in which diabetes, obesity, hyperlipidemia, fatty liver, coronary artery disease, osteoporosis, polycystic ovary syndromes, etc. appear in combination, but also p53 gene-deficient cancers, muscular pain, muscle cytotoxicity and rhabdomyolysis, as well as a preparation method thereof and a pharmaceutical composition comprising the same.