A method of manufacturing a door channel is provided. The door channel is provided in a space defined between an inner panel and an outer panel of a vehicle door and has an outside wall and a connection wall connected to the outside wall. The method includes: (a) disposing the door channel in a die; and (b) forming a cut portion in a comer portion of the door channel by punching the comer portion by a punch. The cut portion includes: a first cut portion formed in a comer portion of the outside wall; and a second cut portion formed in a corner portion of the connection wall and communicating with the first cut portion. By the first cut portion, a first cut surface and a second cut surface facing each other are formed on the outside wall. In the step (b), the first cut portion and the second cut portion are formed by a single punching.