A wiring structure for improving a crown-like defect and a fabrication method thereof are provided. The method includes the following steps. A substrate, on which a seed layer and a patterned photoresist layer with an opening are formed, is provided. A copper layer, having a bottom covering the seed layer, is formed in the opening. A barrier layer covering at least one top portion of the copper layer is formed on the copper layer. An oxidation potential of the barrier layer is greater than that of the copper layer. The patterned photoresist layer is removed to perform an etching process, wherein the copper layer and a portion of the seed layer exposed are etched to form a wiring layer. An immersion process is performed to form an anti-oxidation layer comprehensively on exposed surfaces of the barrier layer and the wiring layer.