Heterogeneous Cu2O/Cu nanoparticles are synthesized by colloidal chemistry approach using ascorbic acid as a reducing agent and polyvinylpyrrolidone as a surfactant. Morphology and structure of Cu2O/Cu nanoparticles are analyzed by SEM, XRD and N2 sorption technique. The catalytic performances of Cu2O/Cu nanoparticles for the degradation of methyl orange (MO) are investigated and reaction kinetics of MO degradation is also studied. The results show heterogeneous Cu2O/Cu nanoparticles display cobblestone-like morphology with ranging from 20 to 40 nm, which are slightly smaller in particle size and higher in BET surface areas than those of pure Cu2O. The Cu2O/Cu nanoparticles demonstrate good potential on degradation of MO because Cu nanoparticles in the Cu2O/Cu hererostructures promote the interfacial charge-transfer kinetics between Cu and Cu2O. High initial MO concentration not only produces low degree of MO degradation, but also increases the reaction time to reach equilibrium, and the degradation reactions follow the pseudo-first-order kinetics model. The Cu2O/Cu catalyst still demonstrates good catalytic activity after four photodegradation cycles of MO solutions.