•Black-ZrO2 thin films were successfully fabricated by simple oxidation.•The black-ZrO2 thin films are composed of equiaxed and columnar grains.•The bandgap of the black-ZrO2 thin films was estimated to be 0.72 eV. Black-ZrO2 thin films were successfully fabricated on the surface of a Zr metal plate by simple oxidation at a controlled temperature in air, under normal atmospheric pressure. The black-ZrO2 thin films were composed of two types of grains with monoclinic ZrO2 structures: 1) fine equiaxed grains with sizes of up to a few hundred nanometers from the surface to a depth of about 5 μm; 2) columnar grains, with long and short diameters of several microns and a few hundred nanometers, respectively, in the inner region above the equiaxed grains. The bandgap of the black-ZrO2 thin films was estimated to be 0.72 eV, based on the Tauc plot using diffuse reflections, which allowed for absorption in the ultraviolet and visible regions of the solar spectrum.