The responsibility of the uteropelvic junction (UPJ) syndrome or abnormalities for renal affections and also for high obstructive uropathy is well-known. But, controversies still remain about the anatomic approach of this clinical feature. Our purpose is to elucidate the developmental anatomy of UPJ and eventually to set the steps of the anatomic approach of the UPJ abnormalities. This study also leads to a better understanding of the mechanism of the intrinsic ureteropelvic junction obstructions. A total number of 122 post-mortem specimens with ages ranging from 1 day to 30 months in both sexes underwent formalin treatment for histological investigation. We performed both transverse and longitudinal sections. Hematein-eosin-safran and Masson's trichrome staining were used. Histological examination revealed that myoarchitecture of UPJ set increasingly up. Circular muscle fibers were first to put in. They had an initial arrangement as a ring in neonates and infants. We conclude that circular layer appears first and sooner than others. On the other hand, coincidence in time between ages of our specimens and ages of patients sufferning from UPJ syndrome leads to further investigations to determine the implication of ring-shaped circular layer in intrinsic ureteropelvic junction obstruction.