ScAlN has high piezoelectricity and ferroelectricity. BAW filters with polarization inverted multilayer structure allow the further improvement of the power durability. In this study, by growing the Al-polar ScAIN film on the N-polar film, the polarization inverted two-layer ScAIN thin films resonator were fabricated. Unusual N-polar ScAIN film was obtained by a polarization inversion treatment to the as-grown usual Al-polar films. Polarity of the ScAlN films was determined by a press test. kt2 of as-grown Al-polar ScAIN and N-polar ScAlN films after the polarization treatment (-190 V (2.0 MV/cm) at 300 °C) were estimated to be 7.7% and 5.6%, respectively. Because of an incomplete polarization inversion, kt2 in the film after polarization inversion treatment slightly decreased compared with the as-grown films. Second overtone mode excitation was observed at GHz range, and fundamental mode was suppressed.