A bicycle handlebar stem includes a body having a connection portion and a top clamp respectively formed on two ends thereof. The body includes a space defined therein, and an opening communicates with the space and outside of the body. A bottom member has a tongue extending inserted into the opening and the space. A bottom clamp is formed to the bottom member and includes an upward portion extending upwardly and toward the downward portion of the top clamp. A passage is defined between the top clamp, the bottom clamp and the body so as to receive a handlebar. A connection member extends through the body and the tongue to connect the bottom member to the body. Two fasteners extend through the underside of the bottom clamp and are connected to the top clamp.