Objectives: This work was conducted to evaluate the role of the relatively newly developed radio-pharmaceutical 99m Tc MAG3 in pediatric renal diseases. Methods: Fifty children with different renal diseases with age ranging from one month up 13 years were subjected to clinical, lab. Assessment [blood urea nitrogen, s. creatinine, urine analysis]; radiological assessment including plain X-ray [all cases] intravenous urography (33 patients) and conventional cystourethrography (for 7 patients with vesico-ureteric reflux); ultrasonography [all cases]; and radio-nucleotide assessment including 99m TC MAG3 examination [all cases] to visualize renal perfusion and generate renogram curves to obtain separate renal function of each kidney; static 99m TC DMSA [25 cases]; and finally indirect radio nucleotide cystography for cases of vesico-ureteric reflux (VUR). Results: When we compared the results we considered each kidney and its ureter separately as a renal unit. 17 renal units showed pelvic-ureteric junction obstruction. False positive obstruction was present in 2 renal units, while there were no cases of false negative obstruction. From the 12 renal units of VUR (shown by micturating cystourthrogram), indirect radio-nucleotide cystography detected 9 units (75%) while the other 3 units (25%) were not discovered. In the renal failure group (10 units) renogram curves showed a plateau pattern (4 units) and a downward sloping pattern (6 units). Four renal units (stone group) showed relative function ranging from 5.5-31.1%. Four renal units with Wilm՚s tumor showed the lesion as a photopenic area with reduced relative function. Multicystic renal disease group (4 units) showed no accumulation of radiotracer. Regarding renal agenesis; ectopic kidney (3 units); and horseshoe kidney (2 cases) 99m TC MAG3 visualized all cases successfully. When comparing 99m TC MAG3 with 99m TC DMSA in detection of scarring, it failed to discover scarring in 3 units visualized by DMSA while MAG3 visualized 7 units of renal scarring not detected by intravenous urography (IVU). Conclusions: 1)-99m Tc MAG3 is an ideal radiopharmaceutical for the investigation and follow-up of obstruction lesions; also for estimation and follow-up of differential and total renal function but is less effective in the detection of focal cortical scarring than 99mTc DMSA. 2)-99m Tc MAG can visualize some renal anomalies (ectopic kidney and renal agenesis). 3)-Finally usage of 99m Tc MAG3 in pediatric filed has no allergic reaction and physiological changes.