Herein, bimetallic Pt-Ir alloy nanoparticles (NPs) were successfully fabricated by ethylene glycol reduction of H2PtCl6·6H2O and IrCl3 through a microwave-assisted method. The Pt-Ir alloy NPs were deposited on CeO2 catalysts for toluene combustion. The Pt2.5Ir/CeO2 sample exhibited better catalytic activity at low reaction temperature, compared with monometallic catalysts. The excellent low-temperature catalytic activity was resulted from the interaction between Pt and Ir, richer adsorbed oxygen species and low-temperature reducibility. Furthermore, the in-situ DRIFTS was used to investigate the possible reaction pathway of Pt2.5Ir/CeO2. It showed that the broken of benzene ring on Pt2.5Ir/CeO2 can be accomplished at lower temperature, resulting in enhancing the deep oxidation of toluene.