A bulk acoustic wave resonator and a filter in which partial thicknesses of protection layers or reflection layers thereof are differently formed are provided. The bulk acoustic wave resonator includes a bulk acoustic wave resonating part comprising a piezoelectric layer, and a reflection layer configured to reflect waves of a resonance frequency generated by the piezoelectric layer based on a signal applied to the bulk acoustic wave resonating part. A thickness of a portion of the reflection layer is different from a thickness of a remaining portion thereof.