Introduction: Total hip arthroplasty has been considered as the operation of the century as it revolutionised the management patients suffering from diseased hip joint.Total hip replacement have demonstrated improved function, reduced pain, and improved quality of lifefor patients, and are cost-effective Hence, the present study was conducted to evaluate functional outcome of 28 mm versus 36 mm femoral head sizes in uncemented total hip arthroplasty.Materials and Methods: The prospective study was carried outamong 80patients who underwent Primary Hip Arthroplasty through posterolateral approach, in the department of orthopaedics. The patients were divided into 2 groups with 40 patients in each group. In one group 28 mm and in other group 36 mm femoral head sizes were implanted during uncemented total hip arthroplasty procedure.The data was statistically analysed by SPSS-22. Results: Among 80 patients, 65% were male and 35% were female. After 24 weeks postoperatively, the flexion was 8.91 degrees, extension was 2.81 degrees, abduction was 5.23 degrees and adduction were 2.2 degrees more in patients who received 36 mm femoral head as compared to the patients who received 28 mm femoral head.The modified HHS was more in patients who received 36 mm femoral head as compared to the patients who received 28 mm femoral head reporting better functional outcome.Wear and tearwas seen in 6 patients of 28 mm and in 2 patients of 36 mm femoral head sizes in uncemented total hip arthroplasty. Conclusion: The present study concludes that uncemented total hip arthroplasty is one of the most effective surgical interventionsthat improves patient’s quality of life by improving range of motion of hip joint post-operatively. The 36 mm femoral heads in total hip replacement revealed better improvement in the rangeof motion hence better functional outcome as compared to use of 28 mm heads in THA.