Pure ZnO and lithium-doped ZnO nanopetals were synthesized via a facile and surfactant-free co-precipitation method. X-ray diffraction results revealed that both synthesized pure ZnO and lithium-doped ZnO exhibited well-crystalline structure. In addition, the lithium ion was successfully doped into ZnO. Field emission scanning electron microscopy showed that the synthesized ZnO was petal-shaped. Lithium-doped ZnO enlarged the band gap of the photocatalysts which was proven by UV–vis diffuse reflectance spectra. The as-synthesized ZnO nanostructures were evaluated for the degradation of phenol under UV–visible light irradiation. The photodegradation of phenol much more rapidly in the presence of lithium-doped ZnO compared to undoped ZnO, revealing that lithium doping improved the photocatalytic activity of ZnO.