A three-dimensional pulsating heat pipe includes a pipe member and a connecting member. The pipe member is coiled around an axis to form a plurality of loop portions, and the loop portions are arranged in order along the axis so as to form a three-dimensional coiled structure. The three-dimensional coiled structure has a heat receiving section, and the pipe member has different effective pipe cross-sectional areas on two opposite sides adjacent to the heat receiving section. The connecting member is connected to two ends of the pipe member, such that the connecting member and the pipe member together form a closed loop.