The long-term thermal-oxidative aging behavior of polyamide 6 (PAIS) Was studied by comparison with the stabilized sample in this work. The variation of mechanical properties of the pure and the stabilized samples of PA6 with aging time at 110 degrees C, 130 degrees C, and 150 degrees C were investigated, respectively. The aging mechanism of PA6 under heat and oxygen was studied in terms of the reduced viscosity, crystallization behavior, dynamic mechanical behavior, and chemical composition through the methods of polarized light microscopy (PLM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray photoelectron energy spectrum (XPS), and so on. The results indicated that at the initial stage of aging, the molecular crosslinking reaction of PA6 dominated resulting in the increase of the mechanical strength, reduced viscosity, and the glass transition temperature of the sample. And the molecular degradation dominated in the subsequent aging process resulting in the decrease of the melting temperature, the increase of the crystallinity, and the formation of the oxides and peroxides products. (c) 2008 Wiley Periodicals, Inc.