This paper presents experimental results on seismic behaviors of post-tensioned (PT) monolithic exterior beam-column connections. Lateral cyclic loading tests were carried out for six fullscale exterior beam-column joint subassemblies fabricated with normal- and high-strength materials. Despite substantial joint cover spalling, the normal-strength specimens exhibited satisfactory lateral strengths and hysteretic behaviors up to ±5% drift ratios by virtue of the confinement effect of post-tensioning. The high-strength PT specimens also showed stable hysteretic behaviors with significantly reduced joint damages. It was found that the post-tensioning can increase the joint shear strength by more than 60% in both types of specimens. Furthermore, the post-tensioning was effective in retaining the lateral stiffness of the beam-column joints under the repeated loads, especially in high-strength specimens, enabling them to maintain at least 90% of their first-cycle stiffnesses throughout the testing.