A microelectromechanical system (MEMS) diaphragm is provided. The MEMS diaphragm includes a first conductive layer, a second conductive layer and a first dielectric layer. The first conductive layer is disposed on a substrate and having a plurality of openings. The openings having a first dimension and the openings having a second dimension are arranged alternately, and the first dimension is not equal to the second dimension. The second conductive layer is disposed between the first conductive layer and the substrate. The first dielectric layer is partially disposed between the first conductive layer and the second conductive layer, so that a portion of the first conductive layer is suspended.