Introduction: Osteoarthritis of knee is more common among all types of arthritic conditions. High tibial osteotomy is an accepted surgical technique for treatment of medial compartment arthrosis of knee in younger patients. Selection of the appropriate patients, extensive pre-operative planning and accurate surgical technique are essential for successful outcome. The methods of high tibial osteotomy include open wedge osteotomy and closed wedge osteotomy, the later procedure being more popular. Aims and Objectives: To assess the functional outcome among patients undergoing high tibial osteotomy. Methodology: A hospital based prospective interventional study was done on 30 patients of osteoarthritis with varus deformity. For all the 30 patients after a proper preoperative assessment the surgical intervention in the form of high tibial osteotomy was done and the outcome was evaluated using knee society scoring system. Results: Among the study population 73.3% of the patients had grade III type of osteoarthritis and only 26.6% had grade IV type of osteoarthritis based on Kellgren and Lawrence type of classification. The mean knee score and the mean functional score of the patients before surgery were 54.6 and 53.9 respectively and post operatively at the end of 12 months the knee score and functional score was 83.1 and 82 respectively. A statistically significant improvement was seen in both the knee society score and the functional score. Conclusion:The main improvements seen in this study was the increase in the knee score and functional score after high tibial osteotomy for the patients of osteoarthritis with varus deformity. Appropriate patient selection, proper osteotomy types and precise surgical techniques are essential for the success of high tibial osteotomy.