The author observed the human fetus kidney at the fetal age of 3 weeks, 5 weeks and 6 month in utero by means of light and electron microscope in order to add some new findings to the already known knowledge. Especially, the metanephros, metanephric blastema, nephrogenic zone of the cortex and blood-urine barrier which consists of glomerulus, capillary vessel, basement membrane, podocyte and mesangium cells are observed and then physiological significance of the kidney are also discussed. On the other hand the fetal kidney change its position from caudal part to the upper part in the lumbar region during development. In this course, when the kidneis are caught by the plexes of the mesenteric artery, developmental retardation of the kidney such as renal hypoplasia, ectopic kidney, fused kidney will occure. The author also described the importance of the study on the developmental embryology, for understanding pathogenesis of abnormal development.