Disclosed herein is pharmaceutical composition derived from pemetrexed dipotassium nonahydrate characterized by X-ray powder diffraction pattern containing at least 5 characteristic 280 diffraction angle peaks selected from the XRPD peak set of 5.0, 12.5, 17.2, 20.8, 22.4, 25.7, 26.9 and 27.9 ± 0.2 2&thetas；°, and a pharmaceutically acceptable amount of an excipient, wherein the pharmaceutical composition having moisture content less than 2%w/w. Also disclosed is a process for preparing lyophilized composition ofpemetrexed dipotassium, comprising the following steps: (a) dissolving a Cryoprotectant (also referred to as &ldquo；generally regarded as safe&rdquo； (GRAS) bulking agents) or a combination of Cryoprotectants selected from mannitol, sucrose, lactose or a combination thereof in water for injection to form a solution； (b) dissolving pemetrexed dipotassium nonahydrate in to the above solution, and determining the pH ofthe solution； (c) adjusting the pH ofthe bulk solution to 7.2 by addition of pH adjusters； (d) make up the volume to 100% with WFI； (e) optionally, filtering the solution obtained in step d)； (f) freezing the solution obtained in step e)； and (g) perform freeze drying to form the lyophilized composition, wherein the composition is having moisture content of less than 2%w/w.
