The development of flexor digital tendon of the hand was studied by electron microscopy in human fetuses ranging from 9 mm to 260 mm crown rump length. The primordium of tendons was first identified as discrete collection of mesenchymal cells at 25 mm fetus. Synovial sheath formation had commenced by 40 mm fetus and was complete by 70 mm fetus. Cell junction or adhesion sites at all ages were noted between the tendon cells. When dilatation of the synovial cavity occurred, two types of synovial cells were observed. A-type cells had numerous vesicles and large vacuoles. In contrast, B-type cells were characterized by abundant rough endoplasmic reticulum and well-developed Golgi complex. By $150mm{sim}260mm$ fetuses, a mojority of the synovial cells were type B. The most remarkable difference between the synovial cells of full-term fetus and adult was the larger amount of collagen fibers in the latter. The vascular buds were first observed between the individual fibril bundles in the interfascicular space at 150 mm fetus. At 25 mm fetus, collagen fibrils were first noted within narrow cytoplasmic recesses which were continued with the extracellular space. Collagen fibrils were filled in almost entire extracellular space at 150 mm fetus. Besides collagen fibrils in the extracellular space small elastic fibers were also identified and followed in their development.