The dynamic responses of a light-weight, high-speedplanar parallel robot are studied based on elastodynamics and experiments. First, according to the geometric and inertial nonlinearities of the mechanism, a set of linear ordinary differential equations of motion is built, and the dynamic responses of two typical configurations are analyzed. Second, an experimental setup that includes the test-bed mechanism of a 3-RRR light-weight parallel robot and a control system is developed. Finally, the experimentally measured residual vibrations of the manipulator are compared with the numerical results. It turns out that the experimental results agree with the numerical ones at configuration two, but differ at configuration one, where the experimentally measured dynamic response is self-excited vibrationand the simulation result is damped vibration. This shows that the robot has different dynamic responses at different configurations.