This invention discloses a positioning device for a bicycle handlebar, wherein a pressing assembly, which is mounted on a front tube, is operated by the user so that it can be pressed against a positioning member, which is fixed to a front fork stem. Since the positioning member is flexible, an elastic resilience relative to the direction of pressing will be produced when the positioning member is pressed to resist the pressing force and the elastic resilience that comes in a reverse direction. As a result, the positioning member and the pressing assembly will be pressed to be positioned. Hence, the front tube will not pivotally rotate relative to the front fork stem, and the bicycle handlebar can be positioned in such a way that the bicycle is unlikely to fall, which also protects the members of the bicycle.