Abstract: A resonant knock sensor includes a housing, a pedestal and a vibration diaphragm. The housing is provided with a support surface therein. The pedestal is fixed in the housing and has a base with a bottom surface attached to the support surface, a support portion protruding from a top surface of the base, and a vibration piece connected to an end of the support portion. The vibration diaphragm is mounted on the vibration piece. As a result, pedestals with different geometric sizes in their support portions or vibration pieces can be selectively assembled with single sized housings and vibration diaphragms to fabricate sensors with different frequency sensibilities at a low manufacturing cost.