Objective: Intramedullary interlocking nail fixation (IINF) for the fracture shaft humerus (FSH) offers good clinical outcome. Evaluating the functional outcome of IINF in FSH and assessing the complications of the technique, time taken for fracture consolidation, and union rates were the objectives.Methods: Adult patients with a clinical diagnosis of diaphyseal fracture of humerus were assessed clinically and radiologically for the functional outcome of IINF in FSH. Functional outcome of shoulder and elbow considered together was graded as excellent, moderate, and poor. Daily assessment was done along with active physiotherapy. All were followed up at monthly intervals for 6-12 months or till the union of fracture. Radiological assessment was done at immediate post-operative period, at months 1, 3, 6, 9, and 12 months.Results: 30 patients (males n=24, 80%) with a mean(±standard deviation) age of 39(±13.31) years were included. Road traffic accident was the frequent cause (n=18, 60%). Indirect injury was the cause in 66.66% patients. Middle 1/3 rd of shaft of humerus was fractured in 53.33% patients. 10 (33.3%) patients each had oblique fracture and transverse fracture, respectively; comminuted fracture was seen in another 26.6% patients. Radial nerve palsy (10%) was the frequent associated injury of the total nine. The overall functional outcome was excellent in 80%, moderate in 16.6%, and poor in 3.3% patients. Postoperatively, nonunion, superficial infection and shoulder stiffness was seen in one patient each. Conclusion:IIFN is an excellent, least invasive surgical option for FHS with early fracture consolidation and better union rates.