This paper introduces a mobile robot named QuadTrack-III developed for urban search and rescue. This robot has four modular tracks which can be driven and lifted independently. Thus the configuration of the robot can be varied for adapting to uneven terrain. Each modular track consists of two sprockets with an attachment chain and two BLDC motors are embedded in the track module. It also includes BLDC motor drivers for each joint. Because the modular track mechanism embodies all of the things required for driving, the weight of the main body is smaller than the tracks. From this feature, the mass center of the robot can be lowered and the distribution of reaction forces can be varied. This paper describes the mechanical structure, the control architecture and a climbing strategy over vertical step for the QuadTrack-III. It also shows some experimental results of the vertical step climbing strategy.