We report on the effects of the polarity of ZnO on the transfer of photogenerated electrons at CsPbBr3 nanoparticle/ZnO heterojunctions. Closely packed CsPbBr3 nanoparticles were coated onto the atomically flat Zn-polar (0001) and O-polar (000 (1) over bar) surfaces of ZnO via spin-coating. The photoluminescence intensity of the CsPbBr3 nanoparticles on the Zn-polar surface was only half of that of the O-polar surface. The lifetime of radiative emission from the CsPbBr3 nanoparticles on the Zn-polar surface also decreased. These results indicate that the polar surface of ZnO clearly affects the recombination of photogenerated electrons from CsPbBr3. This suggests that controlling the polarity of ZnO could be a significant approach for achieving high-efficiency perovskite-based optoelectronic devices, such as light-emitting diodes and photovoltaic devices.