Abstract: A process produces a cationic polymer having a cholesterol-lowering activity, which the process includes a step for subjecting a water-soluble monomer component essentially including a cationic monomer to aqueous polymerization so that the viscosity of a polymerization reaction solution is 1,000 cps or more and less than 300,000 cps at the point of time when a polymerization rate reaches 90%, a step for continuing the polymerization until the polymerization rate exceeds 95%, a step for ultrafiltrating the obtained aqueous polymer, a step for concentrating the ultrafiltration treated solution under reduced pressure at a temperature of the solution lower than 100° C., and a step for drying the concentrated solution under a specific condition. The production process can attain both the safety as a drug and a satisfactory production efficiency.