Pemetrexed is a novel antifolate of antimetabolite with multiple enzyme targets involved in both pyrimidine and purine synthesis. It has entered the clinical usage due to favorable profiles especially in the cancer treatment of mesothelioma and non-small-cell lung carcinoma. But it presents numerous challenges associated with poor water solubility and unstability in its original form of glutamic acid. The aim of this study is to solubilize pemetrexed by designing and synthesizing its aqueous-soluble prodrug using high aqueous-soluble polymeric carrier poly(ethylene glycol) (PEG). A new type of soluble pemetrexed prodrug was synthesized with dihydroxyl PEG and a single amino acid linkage, and was extensively characterized using H-1-NMR, C-13-NMR, Fourier-transform infrared, and matrix-assisted laser desorption time of flight mass spectrometry. In addition, the prodrugs were evaluated for the drug loading capability, the aqueous solubility, and the preliminary in vitro cytotoxicity. The results indicate that the new PEGylated pemetrexed conjugates possess enhanced water solubility and stability, and provide another feasible choice of the pharmaceutical form of pemetrexed in the clinical application. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 444-451, 2009