To provide a method for forming an air chamber for a large-sized float by which a thick latex layer can be formed in a portion of a loose texture and on the inner and outer faces of an air chamberlike body simultaneously.

The method for forming the air chamber for the large-sized float comprises a step of forming a cylindrical body 11 and covering both opening ends of the cylindrical body 11 with a cloth body 12 and providing an air chamberlike body 13, a step of dipping the air chamberlike body into a latex solution 5 and injecting the latex solution into the air chamberlike body, and a step of applying latex coagulation liquid 7 from the outside of the air chamberlike body while rotating the air chamberlike body in a shape holding state. Since the latex solution is soaked into the inner part of the air chamberlike body, and is stuck on the outer face of the air chamberlike body, and the latex coagulation liquid is applied from the outside of the air chamberlike body while rotating the air chamberlike body, a thick latex layer can be formed in the portion of the loose texture, and the air chamber having the thick latex layer on the inner face of the air chamberlike body and a thin latex layer on the outer face can be formed.