Disclosed are: a composition containing an intermediate for a water-soluble monomer, which can be used suitably for the production of a water-soluble poly(alkylene glycol) monomer that has a polymerizable double bond at the terminal, can be used suitably for the production of a water-soluble polymer and enables the production of a water-soluble polymer with high yield; a process for producing the composition; a composition containing a water-soluble monomer, which is produced by the method; a water-soluble monomer which can be used as a raw material for a water-soluble polymer that exhibits an excellent ability of capturing a metal ion such as a calcium ion and a magnesium ion and an excellent anti-gelatinization ability even under high hardness conditions, and has excellent anti-soil-redeposition performance, superior dye-migration-preventing performance compared than those of conventional monomers and excellent compatibility with a surfactant; and a process for producing the water-soluble monomer with higher yield and higher selectivity (in higher purity) compared with those achieved in conventional processes. Specifically disclosed are: a composition containing an intermediate for a water-soluble monomer, which contains a compound (A) having a specific structure, wherein a compound (B) having a specific structure is additionally contained in the composition in a specified amount; and a water-soluble monomer having a specific structure.