Background: Pelviureteric junction obstruction (PUJO) is the most common cause of pediatric hydronephrosis. Objective: To find the relation of renal parenchymal thickness & isotope scan preoperatively & postoperatively in predicting outcome after pyeloplasty. Patients and Methods: This prospective study included, 30 children ≤ 18 years, with 1ry unilateral UPJO from September 2018 to September 2019 were included in the study. Ultrasound abdomen was done on all patients to look at the size of the kidney, parenchymal thickness & renal echogenicity. DTPA scan was done to measure the GFR, t½ and split function of each kidney & all patients underwent open pyeloplasty. Patients were followed up after the operation at 1, 3, and 6 months respectively. At each follow-up visit, U/S was performed & renal isotope was done at the 6^th month. The preoperative parameters were compared with the same parameters after surgical repair of the UPJO at 3rd & 6th months. Results: In our study, there was an improvement in (83.3%) with a significant change in all parameters at 6^th months postoperatively (P < 0.01) as T ½ significantly decreased while parenchymal thickness, GFR of the affected kidney & split renal function were significantly increased postoperatively. Conclusions: This study showed that parenchymal thickness and renal isotope are good predictors for pyeloplasty outcome.