PURPOSE: To obtain a durably functional improved polymer material by treating an active group-having polymer material with a cationic reactive compound and one of various functionality-imparting agents.

CONSTITUTION: This method for producing an improved polymer material having a durable function comprises treating a polymer material having at least one kind of active groups (for example, hydroxyl group, amino group or amide group) with a cationic reactive compound and a functionality-imparting agent for imparting water resistance, water repellency, anti-bacterial property, flame retardance, conductivity, stain resistance, etc., to impart the highly durable function. The cationic reactive compound is a compound having a reactive group capable of forming a covalent bond or an ionic bond to both the polymer material and the functionality-imparting agent, and includes a compound of formula I (R1-R3 are each H, a 1-4C alkyl; X1 is a halogen), for example, glycidyltrimethylammonium chloride, a compound of formula II (R4-R6 are each H, a 1-4C alkyl or an aryl; X2 is X1), such as 3-chloro-2- hydroxypropoxytrimethylammonium chloride.