Medicinal composition for treating cancer

Provided is a liquid medicinal composition formed by containing: (A) pemetrexed, a pharmaceutically acceptable salt or solvate thereof; (B) cysteine, a pharmaceutically acceptable salt or solvate thereof; and (C) a chelating agent. The liquid medicinal composition containing pemetrexed according to the present invention exhibits a suppressed increase of related substances and also suppressed coloring even after long-term storage, so that the composition may be appropriately applied to the treatment of, for example, malignant pleural mesothelioma and non-small cell lung cancer.