A method for fabricating a capacitor is disclosed. First, a substrate is provided, a bottom electrode and a capacitor dielectric layer are formed on the substrate, a conductive layer is formed on the capacitor dielectric layer, a patterned hard mask is formed on the conductive layer, a patterned hard mask is used to remove part of the conductive layer to form a top electrode, the patterned hard mask is removed, and a protective layer is formed on a top surface and sidewalls of top electrode. Preferably, the protective layer includes metal oxides.