A bulk-acoustic wave resonator includes: a substrate; and a resonator including a first electrode, a piezoelectric layer, and a second electrode sequentially stacked on the substrate. The piezoelectric layer is formed of aluminum nitride (AlN) containing scandium (Sc), the content of scandium in the piezoelectric layer is 10 wt % to 25 wt %, and the piezoelectric layer has a leakage current density of 1 μA/cm2 or less.