Abstract: FoldJumper is a foldable wheeled jumping robot. It has two locomotion manners, i.e. rolling and jumping. The former is for rolling on flat surfaces, and the latter is for jumping over obstacles. This robot has a tension spring mounted on each end point of the two foldable legs. In jumping manner, a motor-gear-cam system drives the two legs to extend and the spring stretches to store energy. After releasing of the spring, the two legs fold quickly and the elastic potential energy of the spring is converted into the kinetic energy of the robot to realize jumping locomotion. In rolling manner, the robot moves with two wheels mounted on the end of each leg while the two legs are unfolded. Kinematic and dynamic models of the robot are presented, and the locomotion performances are analyzed by numerical simulations. A prototype of the robot is made, which is about 215g in weight and less than 7cm in length (legs folded). Experimental results show that FoldJumper can jump about 20cm high and 10cm far, while can roll at a speed of 6.5cm/s.