The photoluminescence properties of ZnO/ZnMgO multiquantum wells have been investigated by continuous and time-resolved photoluminescence spectra at various temperatures. Strong first-order and second-order longitudinal optical ~LO!-phonon replicas were observed in the emission spectra. Both the zero-phonon emission and its LO-phonon replicas can be resolved into two components with different temperature dependence. The observation of LO-phonon replicas provided an additional way to characterize the recombination mechanism in quantum wells. Two kinds of excitons are responsible for the resolved emission components and have different coupling strength with LO phonons: one is donor bound excitons which dominated at low temperatures, the other one is the localized excitons due to the well width fluctuation which took over the dominated emission at high temperatures.