A model for predicting time-dependent chloride binding capacity of cement-fly ash cementitious systems was proposed. The proposed model took into account both chemical binding and physical binding. Chemical binding was considered to depend on the amount of unhydrated aluminate and aluminoferrite phases while physical binding depended upon the quantity of hydrated and pozzolanic products. The concept of time-dependent chloride binding capacity was introduced in the model with the consideration of curing time and chloride exposure period. The chloride binding of cement pastes and cement-fly ash pastes under different curing times and chloride exposure periods were tested. Three types of cement and two types of fly ash were used. From the experimental results, time-dependent behavior of chloride binding capacity was observed. At the same chloride exposure period, pastes with longer curing time prior to chloride exposure bound less chloride than those exposed with shorter curing time. Longer exposure period of paste resulted in larger chloride binding capacity. The analytical results from the model were verified with the experimental results from the authors and other researchers. The verification showed that the proposed model was satisfactory for predicting the chloride binding capacity of various cement and cement-fly ash cementitious systems.