A bicycle operating device comprises a base, an operating member, a hydraulic cylinder, a piston, a connecting link, and a guiding structure. The operating member is pivotally coupled to the base. The hydraulic cylinder is mounted to the base. The piston is movably provided in the hydraulic cylinder. The connecting link is pivotally coupled to each of the operating member and the piston to move the piston relative to the hydraulic cylinder in response to a pivotal movement of the operating member relative to the base. The guiding structure is coupled to the piston to guide the piston relative to the base.