[Objective] To compare the therapeutic effect of "on-table" reduced fixation and prosthetic replacement for irreducible Mason type III radial head fractures. [Methods] From January 2005 to January 2017, 27 patients with irreducible Mason type III radial head fractures were treated surgically through "on-table" reduced fixation(11cases) and replacement(16cases). The range of elbow flexion-extension and forearm rotation were compared. The clinical results were evaluated by visual analog scale (VAS), Broberg and Morrey scores. [Results] All patients in both groups received successfully operations. No infection, vascular and nerve injury happened. The operation time and blood loss of the radial head prosthesis replacement group were higher than that of the "on table" reduction and fixation group (P?0.05), while the incision length and hospital stay were not significantly different between the two groups (P?0.05). All the cases were followed up for 18～24 months (20.07±1.84 months on average). There were no complications (such as ischemic necrosis, heterotopic ossification, etc.)in both groups. At the last follow-up, the elbow flexion and extension range, forearm rotation range, Broberg and Morrey score of the prosthesis replacement group were significantly better than that of the "on-table" reduction and fixation group (P<0.05), and the VAS score was slightly lower than that of the "on-table" reduction and fixation group (P?0.05). In the "on table" reduction and fixation group, there were 2 cases of asymptomatic nonunion (1 case of screw rupture and 1 case of screw sliding out), no special treatment after the removal of plate and screws，no loosening in the prosthetic replacement group. [Conclusion] For the treatment of irreducible Mason type III radial head fractures, the prosthesis replacement has more advantages than the "on-table" reduced fixation.