Total talar replacement (TTR) with an additively manufactured personalized total talar prosthesis (TTP) is an emerging treatment for ankle disorders. However, how to enhance the ankle stability after TTR, which usually raises the ankle instability, has not been explored. this study constructed a set of specific numerical models to investigate the effects of TTR and oversized TTPs on the ankle stability, including inversion, eversion, and anterior stability. The oversized TTPs include TTP-FP1.5 and TTP-FP3 scaled the identical TTP0 by 1.5% and 3.0% along the frontal axis, and TTP-VP1.5 and TTP-VP3 scaled TTP0 by 1.5% and 3.0% along the vertical axis. The numerical results identify that under varus/valgus force, the TTP-FP1.5 and TTP-FP3 produce smaller talar tilt angles compared with that of TTP0, as the inversion and eversion stability are significantly enhanced. Furthermore, TTP-VP1.5 and TTP-VP3 can provide larger contact force to the tibia, providing better anterior stability under anterior drawer force. Additionally, the increased contact force of TTP-VP1.5 and TTP-VP3 with the tibial cartilage enhances the eversion stability. Besides, the increase of TTP size along the vertical axis will weaken the inversion stability under low loads, as this scaling might have compromised the stability of the subtalar joint. The present numerical study systematically investigates the effect of different ways of increasing TTP size on ankle stability after TTP.