The ZrO2 and graphitic carbon nitride (g-C3N4) composite photocatalyst has been prepared by calcination process and hydrothermal treatment. The photocatalyst was characterized by x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, UV–vis diffuse reflection spectroscopy, Brunauer–Emmett–Teller and photoluminescence spectra. The photocatalytic activity of the photocatalysts was evaluated by degradation of methylene blue under visible light irradiation. The results showed that the activity of the composite photocatalyst ZrO2/g-C3N4 for photodegradation of MB is much higher than that of either pure g-C3N4 or ZrO2, which is ascribed to the effective electron–hole separation based on the photoluminescence spectra. The •O2
− might be the main active species in MB photodegradation, and the •OH and photogenerated electrons are also partly involved in the process of photocatalytic degradation.