Three-way catalysts (TWC) coated within gasoline particulate filter (GPF) walls (TWC/GPF) were tested in a gasoline direct injection (GDI) engine to investigate the impact of engine oil-derived chemicals on TWC performance and possible deactivation factors. Catalyst performance of the lab-aged TWC/GPFs was retarded with ash loading, especially NOx conversions under 300 degrees C. Characterization results from the lab-aging condition show that while the disruption of oxygen storage capacity (OSC) materials was found to be minor or negligible, Pd particle growth and weakened Pd-OSC interaction were observed. In comparison, the field-aged TWC/GPF showed more apparent degradation of TWC components due to engine-oil-derived chemicals; the formation of CePO4 and Ce-2(SO4)(4) results in decreasing OSC that lowers oxygen release capability, in addition to more noticeable Pd particle growth and weakened Pd-OSC interaction. Different from the lab-aged TWC/GPF, the degree of deactivation in the field-aged TWC/GPF appeared to increase along the direction of the flow path in the order of outlet > mid > inlet, proposing that engine-oil-derived chemicals accelerated TWC deactivation when combined with increased exhaust temperatures.