The chorionic villi tissue of normal term human placentae is made of a highly fibrous extracellular matrix. An increasing amount of fibrous tissue is seen as gestation advances, phenomenon referred as organ aging. Electron microscopy reveals many collagen fibrils close to fibroblasts between the trophoblast and the fetal capillary vessels. A characteristic 67 nm transverse striation produced by the intermixing of tropocollagen and collagen types 1 and 3 is observed. Picrosirius staining under polarized light allowed us to detect abundant type 1 collagen fibers. These were randomly distributed in the stroma but concentrically order around the blood vessels.