The aging impact on oxygen storage capacity (OSC) of three-way catalyst was investigated through experiments and modeling. OSC measurements were conducted on two commercial TWCs (one fresh and one aged) over the temperature window of 100-600 degrees C. The amount of OSC decreased by 44% at 400 degrees C and the kinetic restrictions of OSC reductions extended towards higher temperatures after standard bench cycle (SBC) aging at 955 degrees C for 57 h. The relationship between OSC and temperature was modified. Dynamic OSCs (breakthrough OSC and subsurface OSC) on the fresh and aged TWCs were predicted with a dual-site OSC model. From the modeling results, we found that not only the quantities of oxygen storage sites decreased but also the qualities of storage sites (rate constants) declined after aging. The PGM and surface ceria interface (site S1) declined more severely compared to the sub-surface ceria (site S2). The change of the amount of oxygen storage sites as well as kinetics on the aged TWC sample are reported. From thermodynamic analysis, the alteration of the temperature dependence of OSC is attributed to the change of the thermodynamic properties of ceria.