Ultrasonic vibration was applied to the horizontal plug conveying of granular particles, and the pressure drop was measured. As shown by the results of this experimental research, the pressure loss decreased linearly with increasing ultrasonic vibration regardless of the type of particles and the flow conditions. Therefore, ultrasonic vibration can be used to reduce the frictional resistance between packed particles and the wall surface of a pipe. Additionally, it was shown that this reduction depends on particle velocity. In this study, pressure sensor sheets were attached inside the pipe wall at every 45, and the wall pressure was measured while a plug passed through. If the particle velocity increases, the particles are pushed strongly, spread widely, and the pressure of the particle bed against the pipe wall increases. Eventually, it becomes difficult to float particles and many particles make contact with the pipe surface. Therefore, a large ultrasonic effect cannot be expected under high-velocity conditions. However, this ultrasonic vibration is effective to prevent choking because the pressure loss can be reduced drastically when the particle velocity is slow. (C) 2016 Elsevier B.V. All rights reserved.