A method of fabricating a through silicon via (TSV) structure is provided, in which, a first dielectric layer is formed on the substrate, the first dielectric layer is patterned to have at least one first opening, a via hole is formed in the first dielectric layer and the substrate, a second dielectric layer is conformally formed on the first dielectric layer, the second dielectric layer has at least one second opening corresponding to the at least one first opening, and the second dielectric layer covers a sidewall of the via hole. A conductive material layer is formed to fill the via hole and the second opening. The conductive material layer is planarized to form a TSV within the via hole. A TSV structure is also provided, in which, the second dielectric layer is disposed within the first opening and on the sidewall of the via hole.