In this paper, we report on a direct measurement of the vibration on the surface of a droplet during its sliding on a micropillar array. The measurement is realized by using a MEMS-based force sensor fabricated under a micropillar Our method provides direct information on the frequency of the vibration which was difficult to be obtained by conventional observation-based methods. We demonstrate that in case of a water droplet sliding on a 125 mu m-pitch micropillar array, a vibration at frequency of approximately 3 kHz was found to occur on the droplet surface. Moreover, we show that the frequency of the vibration during the sliding of a droplet on a micropillar array does not depend on the sliding velocity nor the volume of the droplet.