A control module, which is mounted on a handlebar of a bicycle, includes a base, a grip, a control bar, and a bolt. The base has a hole, and the hole has a first section and a second section, wherein the second section is bigger than the first section. The base is fitted to the handlebar whereby a sidewall of the first section touches the handlebar. The grip is fitted to the handlebar, and has a portion received in the second section of the hole of the base. The control bar is provided on the base to control a brake module or a derailleur module. The bolt is provided on the base, wherein both the base and the grip are fixed to the handlebar at the same time by tightening the bolt.