The present invention provides a composition for treating hair, skin, or fiber, comprising a cationic cellulose polymer. In the present invention, the cationic cellulose polymer may be used for various purposes by adjusting the molecular weight.Specifically, the present invention provides the use of the cationic cellulose polymer for imparting flexibility to hair, skin, or fiber, the use for cumulatively adsorbing active ingredients onto hair, skin, or fiber by allowing the active ingredients to be bound to the cationic cellulose polymer, the use for transferring active ingredients to hair, skin, or fiber by allowing the active ingredients to be bound to the cationic cellulose polymer, and the use of the cationic cellulose polymer, a crosslinking-mediating component having a carboxyl group or amine group, and a carbodiimide-based compound for preventing the loss of hair, skin, or fiber components.