The invention relates to water-soluble polymers reduced in molecular weight, a process for production of the same, and usage thereof. It makes it possible to obtain water-soluble polymers reduced in molecular weight by a simple procedure and in an economical and simple manner by subjecting either an aqueous solution admixed with an aqueous solution of an oxidizing agent and containing an amount within the range of 10-60% by mass of a water-soluble polymer and having a viscosity of not lower than 3000 mPas or a granular composition admixed or impregnated with an aqueous solution of an oxidizing agent and containing an amount within the range of 10-60% by mass of a water-soluble polymer to oxidation reaction, not by the method of polymerization at elevated temperatures, which is an energy-consuming method, or by the method of polymerization using large amounts of a chain transfer agent and/or an initiator, which is one of the raw materials, and these water-soluble polymer reduced in molecular weight can be used fixing agents for improving the water resistance and/or light fastness of printed matters and, further, the solution viscosity of this water-soluble polymer reduced in molecular weight can be adjusted, hence the handleability thereof, among others, can be adjusted, by incorporating a water-soluble salt and/or a polymer additive in these water-soluble polymers reduced in molecular weight to give compositions comprising the water-soluble polymer reduced in molecular weight.