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The rotational speed sensor is utilized to measure the rotational speed of rotating objects, finding widespread application in fields such as automotive engineering, industrial equipment, motor control, and aerospace to enable operational monitoring and fault diagnosis. This letter presents a sensitive unit composed of magneto-sensitive elastomer (MSE) and polyvinylidene fluoride (PVDF), hereinafter referred to as MPSU. Owing to the excellent magneto-sensitive properties of MSE, the PVDF component within the designed MPSU generates a piezoelectric effect when the MSE was exposed to a magnetic field. The rotational speed can be determined by processing the periodic piezoelectric output voltage signal. Dynamic magnetoelectric performance tests of the MPSU and rotational speed detection experiments at a constant speed of 2400 rpm were conducted to verify its sensing capability. The experimental results demonstrate that, compared with conventional Hall sensors, the proposed MPSU not only achieves accurate rotational speed detection but also enables self-powered operation. Therefore, this sensor design concept significantly expands the potential applications of rotational speed sensing technology.