This thesis presents the development of a mobile manipulator system, which was used to assist the picking task in an automatic warehouse system. Three major research topics were included in the research: design and implement of mobile manipulator system, development of motion control system, and implement of application examples. First, according to the design requirement of the mechanism, the mechanisms of robot manipulator, mobile platform, and the end effector were planned and designed. Second, the appropriate motors were selected for the drive system of the manipulator and mobile platform. Meanwhile, the kinematics of the manipulator and mobile platform were also analyzed for kinematic control purposes. The control system was developed in the Robot Operating System (ROS) environment to take advantage of its open source and architecture integrity. Finally, several application examples were carried out to validate the performance of the developed mobile manipulator system, including the performance tests of individual modules: the mobile platform, the robot manipulator, and the end-effector. The picking task of the integrated mobile manipulator system were also tested.