An automatic approach based on microscopic visual control is proposed for a microassembly task, which is to insert a 10-μm-diameter glass tube into a 12-μm-diameter hole on a silicon substrate. A three-degree-of-freedom manipulator is used to control the motion of the glass tube. A microscopic camera is mounted on a movable platform toward the hole in the inclined direction ∼30 deg from horizontal plane in order to view the hole and the tube. A calibration method based on active motions is designed to estimate the intrinsic and extrinsic parameters of the microscopic camera, which includes only two steps of motion of the tube’s tip on the focal plane of the microscopic camera. The relative position errors are computed from the image feature errors and the parameters of the microscopic camera. A position-based control strategy is applied to align the tip to the position above the hole, which controls the tip to move to the hole alongx , y , and z axes simultaneously. The tip is moved down a specified distance to insert into the hole after autofocus in order to improve the insertion accuracy. The experimental results verify the effectiveness of the proposed method.