End effectors of laser ablation systems for minimally invasive surgery are crucial to the performance of integrated laser ablation systems. Due to the constraints imposed by millimeter-sized overall diameter, the designs of laser ablation end effectors are challenging. In this paper, a laser ablation end effector for minimally invasive surgery is designed and built. The proposed end effector is composed of a bending section, a ball joint mechanism and a micro imaging sensor. By actuating the bending section and the ball joint mechanism independently, the Nd:YAG laser beam with the wavelength of 1064nm is steered to desired directions within its workspace and irradiate target lesion points. The diameter of the laser ablating distal module is 5 millimeters and the maximal tilt angle of the ball joint mechanism is 26 degrees. Furthermore, based on the proposed end effector and auxiliary mechanical system, an autonomous laser ablating approach is established to coagulate lesion. This method is developed on a lesion's planar contour which is obtained by the small image sensor, and the coordinates of all planned ablating positions are calculated, satisfying that all lesion area are covered. The laser ablating method is verified by experiments.