Objective The objective of this study is to measure renal function improvement after endopyelotomy for secondary pelvi-ureteric junction (PUJ) obstruction using technetium-99m diethylene-triamine-pentaacetate (DTPA) renal scintigraphy. Material and methods This descriptive study was carried out at the Department of Urology, Institute of Kidney Diseases, Peshawar, Pakistan from June 1, 2021, to May 31, 2023. The study included 118 secondary PUJ blockage patients who underwent endopyelotomy. Patient demographics, clinical history, and preoperative imaging findings were obtained. DTPA renal scintigraphy assessed renal function improvement postoperatively at intervals to determine the efficacy of endopyelotomy. Results The majority of the patients included in the study were male (n=65, 55.1%). The average age of the patients was 45.2 years, with the majority falling within the age range of 46-60 years (n=42, 35.6%). All patients had ultrasonography and computed tomography imaging done, and preoperative renal functions were obtained. Comorbidities included hypertension in 32 (27.12%) and diabetes in 18 (15.25%). DTPA renal scintigraphy showed improved renal function in 81.35% of patients at three months, 88.13% at six months, and 83.05% at 12 months; 15.3% of patients needed further treatments, and 5.1% had PUJ blockage recurrence. Conclusion This study offers significant insights into the results and complexities of endopyelotomy in patients suffering from PUJ blockage. The findings indicate that the technique efficiently enhances kidney function and alleviates symptoms in most patients. However, the study also emphasizes the need to monitor patients undergoing this procedure.