A method for fabricating a blind via structure of a substrate is provided. First, a substrate is provided, which includes a conductive layer, a metal layer, and a dielectric layer disposed between the conductive layer and the metal layer. Next, a cover layer is formed on the conductive layer. Finally, the substrate formed with the cover layer is irradiated by a laser beam to form at least one blind via structure extending from the cover layer to the metal layer. The blind via structure includes a first opening, a second opening, and a third opening linking to one another. The first opening passes through the cover layer. The second opening passes through the conductive layer. The third opening passes through the dielectric layer. For example, a size of the first opening is greater than a size of the second opening and a size of the third opening.