A method for making bicycle frames includes a step of preparing a seat tube and a head tube and both of which are then put in concavities of two first movable mold parts on a base board. A top tube and a down tube are prepared by carbon-fiber sheets and connected between the seat tube and the head tube. Two connection ends made by carbon-fiber sheets are connected to the seat tube. Two second movable mold parts are mounted to the first movable mold parts and air is then blown into the top tube, down tube and the two connection ends to inflate the carbon-fiber sheets to contact against inner peripheries of the concavities under high temperature and pressure to let the carbon-fiber sheets be solidified.