An apparatus for diagnosing the characteristic of an acceleration sensor and a method for diagnosis thereof are disclosed. The acceleration sensor includes a movable electrode (or mass part) displaced in accordance with an acceleration and a fixed electrode disposed opposite to the movable electrode. In a diagnosis mode, a signal for diagnosis is applied to the fixed electrode so that an electrostatic force as a force corresponding to a predetermined acceleration is generated between the fixed electrode and the movable electrode. In the case where the acceleration sensor is sound, the movable electrode or mass part is normally displaced. A failure of the acceleration sensor, the deterioration thereof in performance, a change in characteristic thereof caused from the lapse of time, or the like is self-diagnosed by detecting a change in capacitance between the movable electrode and the fixed electrode upon generation of the diagnosis signal. The force corresponding to the predetermined acceleration may be an electromagnetic force or a mechanical oscillation based on a piezoelectric element.