Time-resolved photoluminescence has been used to study the effects of interface roughness on excitonic transitions in GaAs-AlxGa1-xAs multiple quantum wells. In addition to the luminescence linewidth broadening and Stokes red shift, the interface roughness also strongly affects the dynamic process of optical transitions so that the excitonic transition peak shifts with delay time. However, the heavy-hole exciton transition has red shifts at short delay times and exhibits a turnover at longer delay times. A maximum shift of about 0.1 meV at a delay time of 4 ns was obtained. We have demonstrated that the peak shift is caused by interface roughness in the quantum wells. Furthermore, the decay of the excitonic transition is found to fit a two-exponential form. Based on a model involving interface roughness and two-exponential decay, we calculated the position of the excitonic transition peak as a function of delay time. Our calculations are consistent with experimental results.