An oil seal bearing of a fan includes a ring-shaped body for supporting a shaft of the fan, and a protruded portion disposed on the ring-shaped body. The protruded portion has a first slope, wherein the first slope is disposed corresponding to an inner top surface of a hub of the fan. An oil storage space is formed between the first slope, the shaft and the inner top surface for storing a lubricant. A first angle is formed by the extension of the first slope and the inner top surface, such that the lubricant is retained by the capillarity between the first slope and the inner top surface. Under this circumstance, the oil sealing is achieved without any additional oil seal, the effective bearing height is maximized, and the advantages of enhancing the supporting efficiency and lengthening the lifetime of the product are also achieved.