To recycle waste cellulosic materials and post-consumer disposal-synthetic polymers, various composites of the high density polyethylene (HDPE) with maple woodflour have been prepared with maleic anhydride as compatibilizer and magnesium hydroxide as flame-retardant agent. The thermal behaviors of these composites in nitrogen and air have been investigated. The effects of the addition of maleic anhydride and magnesium hydroxide on the composite matrices have also been studied by TG-DTA.