Patients with proximal humerus fractures were treated with open reduction and internal fixation using a locking plate between March 2016 and February 2023 in a randomized controlled trial. Fifty-five patients were randomized to either a conventional rehabilitation group with four weeks of sling immobilization or an early active motion group with no movement restrictions. After losses to follow-up and predefined exclusions due to complications or revision surgery, 40 patients (20 per group) were included in the final analysis. The primary outcomes were Constant Score (CS), relative constant score, and Disabilities of the Arm, Shoulder and Hand (DASH) score. Secondary outcomes included pain (VAS), patient satisfaction, and health-related quality of life (EQ-5D-VAS). Outcomes were assessed at multiple time points up to 24 months postoperatively. Overall, the results of the study revealed no statistically significant differences between groups in CS, relative constant score, DASH score, pain, patient satisfaction, or EQ-5D-VAS at any follow-up point. These findings indicate that early active motion rehabilitation is not inferior to a restrictive postoperative protocol following locking plate fixation of proximal humerus fractures.