Many existing reinforced concrete (RC) bridge piers do not have sufficient seismic-resistant capacities during the long-term service period. Seismic retrofitting of these piers will be an impending problem. In this study, quasi-static cyclic tests were conducted to investigate the efficiency of ultra-high performance concrete (UHPC) in strengthening the seismic performance of RC bridge piers. Three test specimens, among which one is a normal RC pier and the others are UHPC jackets-retrofitted RC piers, were used for the cyclic tests. Based on the experimental results, the effects of UHPC jackets on hysteresis response, strength, ductility, stiffness degradation, energy dissipation, residual displacement, and curvature distribution, are analyzed and discussed. The results show that after being retrofitted by UHPC jackets, the curvature distribution and damage modes of the RC pier are changed, and the strength and stiffness are improved. Furthermore, 50 mm-thick UHPC jackets contribute to a significant reduction of residual displacement and equivalent viscous ratio, indicating improving post-earthquake serviceability of retrofitted piers. Numerical simulation was conducted to further investigate the influence of size of UHPC jacket on the envelope curve for the RC pier. It was found that for a fixed thickness or height of UHPC jacket, the strength of retrofitted pier would not increase with the UHPC jacket volume when it reached to a certain value.