Thermal degradation of maleic anhydride grafted polyethylene (manPE) in nitrogen and in air was studied by thermogravimetry and differential scanning calorimetry. The decomposition temperature of manPE in nitrogen shifted to a higher value with increasing heating rate, but a complex thermal phenomenon was observed when manPE decomposed in air. Chain scission and crosslinking are proposed as two counteractive factors to determine the decomposition temperature in air. Radical species (R-.) and hydroxyl groups (ROH) form when manPE degraded in air. The radical species accelerate the oxidative degradation, but ROH could react with the maleic anhydride groups to form a stable crosslinking structure. Both slow heating and prolong heating at 220 degrees C allow the stabilizing reaction to proceed to a higher degree between ROH and the maleic anhydride groups and lead to enhanced thermal stability of manPE.