An adjustable positioning structure of a bearing of a bicycle wheel rim contains: a central shaft, two screw nut devices, two bearing caps, two fitting sleeves, two fixers, and two abutting elements. The central shaft includes two threaded portions. Each screw nut device includes two screw nuts for adjusting a length of the central shaft. Each bearing cap includes a through orifice. An internal ring of each fitting sleeve is fitted into each bearing cap. Each fixer is disposed on each fitting sleeve. Each screw nut device is configured to position an internal ring of each fitting sleeve to adjust a working length of the hub. Each abutting element is fixed on each fixer to connect the central shaft, each bearing cap and each fitting sleeve on the hub, thereafter the hub is locked on a bicycle rack or a front fork of a bicycle.

An adjustable positioning structure of a bearing of a bicycle wheel rim contains: a central shaft, two screw nut devices, two bearing caps, two fitting sleeves, two fixers, and two abutting elements. The central shaft includes two threaded portions. Each screw nut device includes two screw nuts for adjusting a length of the central shaft. Each bearing cap includes a through orifice. An internal ring of each fitting sleeve is fitted into each bearing cap. Each fixer is disposed on each fitting sleeve. Each screw nut device is configured to position an internal ring of each fitting sleeve to adjust a working length of the hub. Each abutting element is fixed on each fixer to connect the central shaft, each bearing cap and each fitting sleeve on the hub, thereafter the hub is locked on a bicycle rack or a front fork of a bicycle.