The roles of the two substructures of the striatum, i.e., caudate and putamen, in voluntary motor control are less addressed. The present functional magnetic resonance imaging (fMRI) study investigated the neural correlates of motor control while participants were asked to press with their right index finger, and to hold naturally, and then to relax, and we focused on whether the caudate and putamen were involved differently during the pressing, holding, and relaxation of the finger. Only the bilateral caudates were activated in the holding process, i.e., sustaining of the muscle contraction, and only bilateral putamen were activated in the relaxation process, along with subthalamus nucleus (STN). However, both the caudate and putamen were activated in the pressing process. We conclude that the two substructures of the striatum, i.e., caudate and putamen, play different roles in motor control; the caudate plays a more important role in muscle contraction, while the putamen plays a more important role in muscle relaxation. However, they cooperate together to accomplish a successful and smooth movement, in line with the modulation role of the basal ganglia in motor modulation.