We synthesized Au nanoparticle (AuNP)/ZnO composite particles in presence of an anionic surfactant and evaluated their photocatalytic activity under visible-light irradiation. AuNPs synthesized from HAuCl 4 in the presence of amylase and the precursor solutions of ZnO were mixed, followed by a hydrothermal process, to synthesize crystal face-controlled AuNP/ZnO composite particles. X-ray diffraction (XRD) patterns and ultraviolet-visible (UV-Vis) spectra confirmed the formation of AuNP/ZnO composite particles. Furthermore, different Au to Zn concentration ratios in the precursor solutions resulted in different amounts of AuNPs in the composite particles. In addition, the average size of the AuNP/ZnO composite particles decreased with increasing Au to Zn concentration ratio. We believe AuNPs act as the nuclei for ZnO particle formation. The photocatalytic activity of the AuNP/ZnO composite particles was evaluated by the photodegradation of methylene blue (MB) under visible-light irradiation. The photodegradation rate of MB was higher with AuNP/ZnO composite particles compared to that with the ZnO particles synthesized in the absence of AuNPs. The AuNP/ZnO composite particles exhibit photocatalytic activity under visible-light irradiation owing to the enhanced charge separation efficiency and the localized surface plasmon resonance effect.