A method of fabricating a capacitor structure includes the following steps. Firstly, a substrate is provided. A first conductive layer, a first insulation layer, a second conductive layer and a second insulation layer are sequentially formed over the substrate. A hard mask material layer is formed on the second insulation layer. Then, the hard mask material layer is defined with a photo resist pattern, so that a hard mask is formed. After the photo resist pattern is removed, the second conductive layer is defined with the hard mask, so that a first electrode of the capacitor structure is formed.