The present invention relates to a stabilized pemetrexed formulation, and more specifically, to a stabilized pemetrexed formulation comprising acetylcysteine as an antioxidant and sodium citrate as a buffering agent. Additionally, the present invention relates to a pemetrexed formulation filled in a sealed container, comprising pemetrexed or a pharmaceutically acceptable salt thereof as an active ingredient, wherein the oxygen gas content within the headspace of the container is 3 v/v % or less.
