PROBLEM TO BE SOLVED: To provide a wire coating material, an insulated wire, and a wire harness a diameter of which can be reduced and which enable insertion into a terminal without being buckled when used as an insulated wire, as well as satisfying flexibility and having an excellent appearance of a wire.SOLUTION: The wire coating material containing 100 pts.mass of a polyvinyl chloride, 10 to 20 pts.mass of a plasticizer, 1 to 6 pts.mass of a chlorinated polyethylene, and 1 to 6 pts.mass of a MBS resin such that a total amount of the chlorinated polyethylene and the MBS resin is 2 to 7 pts.mass is used to coat a conductor 1 such that a thickness of an insulator 2 is 0.25 mm or less, and resulting in obtaining an insulated wire 1 having an outer diameter of below 1.1 mm.