Present invention relates to a stable pharmaceutical composition comprising intimate mixture of alogliptin and metformin, and suitable pharmaceutically acceptable excipient/s; wherein metformin is present in about 3.3 parts or more parts by weight relative to 100 parts by weight of the total weight of part comprising alogliptin. Invention also encompasses various processes of preparing said pharmaceutical composition and its use in improving glycemic control in adults with type 2 diabetes mellitus.