A braking system is mounted on a rollator or a transport chair and includes a braking part and an operating system. The braking part is mounted adjacent to a wheel of a rollator or a transport chair. When the operating system is unactuated, the braking part abuts a corresponding wheel to avoid a rotation of the corresponding wheel. When a user wants to walk and move the rollator or the transport chair, the user can press the operating system such that the braking part departs from the wheels and releases a brake. When the user wants to sit on the seat cushion and rest, the user can keep the braking system actuated without pressing the operating system, and accordingly the rollator or the transport chair would not be slidable when sat on, thereby avoiding danger. In addition, when the user walks on a slope, the user can release their hands from the rollator or the transport chair without making the rollator or the transport chair slide down the slope.