A needle-holding robot for microwave ablation therapy is developed to free two hands of the surgeon, so that more effort can be concentrated on monitoring the ablation procedure, which in turn guarantees good tumor ablation effect. The overall architecture of the robot is introduced first with the explanation of the mechanism of 3D motion tracking and how to minimize damping force for the robotic hand. Two experiments were conducted, one to quantify the force required for motion tracking, the other to assess the performance of motion tracking. The results of force-measuring experiment show that the force required for rotation and radial translation motion tracking are less than 15 grams, which indicates the high sensitivity of the holding robot. The results of in-vivo animal test performed on a swine show that the holding robot is accurate enough in tracking the 3D motion of the ablation needle, which allows for stable and precise holding of the needle compared to that of freehand holding.