The present invention relates to a composition of a ready-to-use injectable solution, comprising pemetrexed or pharmaceutically acceptable salts thereof, which comprises pemetrexed, sodium sulfite, and N-acetyl-L-cystein. With respect to use as an injectable preparation, the composition of a ready-to-use injectable solution comprising pemetrexed in accordance with the present invention is suitable for effective administration of pemetrexed since melting process of the main components before administration is not necessary, and the composition can be used by being diluted immediately in a perfusate. In addition, the properties of the composition do not change even in long-term storage, and pharmaceutical stability is significantly improved by inhibiting related substances below a standard, therefore the composition can be stored in a liquid preparation state.
