To develop and provide a method for keeping durability of the gut of a racket by which the gut is protected by keeping a twist and elasticity in a racket and also durability is raised in the racket.

A coating agent (1) such as a fluorocarbon resin or 100% silicon is lightly applied with the sponge (Z) of a public applying tool (2) onto the both surfaces of the gut (Y) strung in the racket (X) and then, wiped away with a cloth, etc. Thus, durability is kept in the gut by the method.