Abstract: Posttensioning self-centering (PSCR) bridge pier is a seismic-resilient structural system characterized by self-centering capability, high energy dissipation capacity and enhanced seismic performance. The self-centering behavior is achieved through unbonded posttensioning (PT) tendons, while supplemental energy dissipation (ED) devices are employed to improve ED. To investigate the three-dimensional (3D) rocking motion characteristics and failure mechanisms of PSCR piers under seismic excitations, this study establishes a 3D rocking motion analysis model using Euler angles and Lagrange’s equations in which the face-to-face rocking contact at the pier base and the rolling energy dissipation during contact are included. Based on this model, three additional rocking system variants are derived: the ED system (w/o PT tendons), the PT system (w/o ED bars) and the purely rocking system (w/o both PT tendons and ED bars). A comparative analysis of the 3D rocking responses of these systems is conducted to reveal the pier’s seismic failure mechanisms. A parametric study is performed to assess the influence of contact stiffness and ED on the spatial displacement trajectories, PT tendon forces and ED bar strains. The results indicate that the seismic rocking response of PSCR piers exhibits obvious spatial effects, where the precession angle φ determines the trajectory direction, while the nutation angle θ controls the displacement amplitude. Both PT tendons and ED devices effectively reduce displacements and mitigate overturning risks. Large contact stiffness causes the pier to transition from 3D rocking to high-frequency vertical micro-vibrations, whereas large contact damping suppresses the ED of bars, preventing their yielding.