In this study, we assessed and compared the outcomes of two different fixation techniques for humeral diaphyseal fracture nonunions. A retrospective evaluation of 22 patients who underwent single-plate and double-plate fixation due to humeral diaphyseal nonunions was conducted. Union rates, union times, and functional outcomes of the patients were assessed. There was no significant difference between single-plate and double-plate fixation in terms of union rates or union times. The double-plate fixation group achieved significantly better functional outcomes. Nerve damage or surgical site infection were not encountered in either group.Due to its considerable effect on stability, double-plate fixation, offers both patients and surgeons confidence in terms of early adaptation to daily life in the postoperative period.