A measuring device for a pedal plane angle of a bicycle includes a pedal body, an angle sensing unit and a central processing unit (CPU). The angle sensing unit is disposed in an accommodating chamber of the pedal body, and senses an angle of the pedal body to send an angle sensing signal. The CPU analyzes the angle sensing signal to obtain angle data of the pedal body relative to an angle of a reference plane to accordingly learn an angle relationship between the pedal body and the reference plane. The angle relationship may coordinate with other sensing units, for example, data of a pedaling force sensing unit to mutually correct and analyze the data, so as to obtain correct pedaling force information. With the angle data, whether a pedaling angle of a rider is correct can be learned to prevent sports injuries caused by incorrect pedaling angles.