A method for fabricating a MEMS is described as follows. A substrate is provided, including a circuit region and a MEMS region separated from each other. A first metal interconnection structure is formed on the substrate in the circuit region, and simultaneously a first dielectric structure is formed on the substrate in the MEMS region. A second metal interconnection structure is formed on the first metal interconnection structure, and simultaneously a second dielectric structure, at least two metal layers and at least one protection ring are formed on the first dielectric structure. The metal layers and the protection ring are formed in the second dielectric structure and the protection ring connects two adjacent metal layers to define an enclosed space between two adjacent metal layers. The first dielectric structure and the second dielectric structure outside the enclosed space are removed to form a MEMS device in the MEMS region.