The present invention has an object to provide a polymer-containing composition for dispersants for cement which exhibits higher cement dispersibility even when used in a small amount, and can provide high flowability to a cement composition such as mortar and concrete and stably maintain this high flowability for a certain period, and to provide a production method thereof. The polymer-containing composition for dispersants for cement includes a polymer including a repeating unit derived from an unsaturated polyalkylene glycol ether monomer (I) having a specific structure and a repeating unit derived from an unsaturated carboxylic acid monomer (II) having a specific structure, and is prepared by polymerizing an unsaturated polyalkylene glycol ether monomer (I)-containing composition that includes specific amounts of specific components.