A kind of rare earth compound, ytterbium trifluoromethanesulfonate (Yb(OTf)(3)), was introduced into high-density polyethylene (HDPE) by melt compounding to investigate the effect of Yb(OTf)(3) on the thermal and thermo-oxidative stability of HDPE. The results of thermogravimetric (TG) and differential scanning calorimetry (DSC) showed that the addition of Yb(OTf)(3) made the thermal degradation temperatures dramatically increased, the oxidative induction time (OIT) extended, and the enthalpy (Delta H-d) reduced. Very low Yb(OTT)(3) loading (0.5 wt%) in HDPE could increase the onset degradation temperature in air from 334 to 407 degrees C, delay the OIT from no to 24.3 min, and decrease the Delta H-d from 61.0 to 13.0 J/g remarkably. Electron spin resonance spectra (ESR), thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TGA-FTIR), rheological investigation and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) indicated that the free radicals-trapping ability of Yb(OTf)(3) was responsible for the improved thermal and thermo-oxidative stability. (C) 2015 Elsevier B.V. All rights reserved.