A Cu2O@TiO2 core-shell heterojunction photocatalyst was prepared by an in situ hydrolysis and crystallization method. The as-prepared catalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. Under simulated sunlight irradiation, it exhibited high photocatalytic activity and stability for 4-nitrophenol (4-NP) degradation. Compared with neat Cu2O and Cu2O/TiO2(PM) prepared by physical mixing, the heightened photocatalytic activity of Cu2O@TiO2 was attributed to the improvement of charge separation since large close interface was formed between the two semiconductors. The in situ method may generally be applied to develop other core-shell heterojunction photocatalysts. (C) 2011 Elsevier B.V. All rights reserved.