The present invention relates to a combination formulation containing metformin for treating non-insulin-dependent diabetes and an HMG-CoA reductase inhibitor for treating dyslipidemia. The present invention provides a combination formulation and a method for preparing the combination formulation, wherein the combination formulation contains metformin and an HMG-CoA reductase inhibitor, and has effectively improved stability by blocking physical and chemical reactions between the active ingredients while securing the stable release of respective active ingredients.