This paper proposes a design and implementation of an assist-mode, hybrid electric motorcycle (H.E.M.). The proposed hybrid electric motorcycle is a revised vehicle from a 50 cc motorcycle and designed to match up with a 100 cc motorcycle. In order to expedite the developing phase and lower down the cost, a master-slave tracking control method is utilized. A dc servo-motor is deployed to track the speed of the rear wheel of the motorcycle and to provide more torque through power composite into the rear wheel so that the performance of hybrid electric motorcycle can be promoted. The advance of performance as well as the energy saving can both be expected. In road trip experiment, the H.E.M. prototype achieves an average gasoline mileage of 46 km 1(-1) compared to the original 34 km 1(-1). The overall efficiency is about 35% lift. Experimental results confirm the feasibility and prosperities of the proposed hybrid electric motorcycle. (c) 2007 Elsevier B.V. All rights reserved.