Recycling discarded rubber is important for both environmental and economic reasons. One of the most attractive methods of recycling rubber waste is to use ground rubber (GR) as a compounding ingredient or as a replacement for raw polymers. In this study, ground natural rubber was prepared with different curing systems and compounded into the parent compounds. The cure behaviors and physical properties of the GR-filled vulcanizates were investigated, and they were largely affected by the curing systems of the rubber matrix and GR. GR-filled vulcanizates with GR and the rubber matrix, having a conventional curing system, showed the largest changes in the cure characteristics. The greatest decrease in the physical properties was observed for peroxide-cured-GR-filled vulcanizates. The addition of GR decreased the crosslink density of the GR-filled vulcanizates. This was thought to be the main reason for the reduction of the mechanical properties of the GR-filled vulcanizates. However, the adhesion between the GR and rubber matrix may also have caused the differences in the physical properties of the GR-filled vulcanizates with respect to the curing systems of the rubber matrix and GR. (c) 2007 Wiley Periodicals, Inc.