M/Cu₂O (M = Ag, Au) heterogeneous nanocrystals are successfully prepared by depositing noble metal nanoparticles onto the surfaces of Cu₂O octahedral nanocrystals through a simple photocatalytic process. The samples are characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). The influence of the light source and solution temperature on the deposition of noble metal (taking Ag as an example) nanoparticles has been studied. The experimental results show that visible light is more favorable for the deposition of Ag nanoparticles onto Cu₂O nanocrystals, and a solution temperature of more than 30 °C can prevent the erosion of Cu₂O. The photocatalytic properties of the prepared M/Cu₂O heterogeneous nanocrystals are studied, showing enhanced photocatalytic activities.