Dynamic rheological analysis and Fourier transform infrared spectroscopy (FTIR) were used to study the effects of thermo-oxidation on the viscoelasticity and microstructure of polyolefin elastomers (POE). It was found that dynamic storage modulus (G′) and dynamic loss modulus (G〞) at low frequency region can sensitively reflect the change of microstructure of POE, which can be seen through the “second plateau” appeared in G′ versus #61559; plots at low frequencies. The frequency dependence of loss tangent (tanδ) measured under different frequency sweeps showed that the thermo-oxidative behaviors of POE relied on the holding time. The dynamic rheology test was found to be a sensitive technique for analyzing the structural changes during thermo-oxidation of polymers.