Ground rubber powder (GRP) and devulcanized rubber (Dev.R) waste through a continuous shear-flow reaction were used as fillers for virgin natural rubber. A Horikx plot and the gel fraction proved that both main-chain scission and crosslink scission occurred during the devulcanization. The cure characteristics, swelling behavior, crosslink density, and mechanical properties were studied. GRP and Dev.R, generated from passenger car and light truck tires, showed applicable mechanical properties in the new rubber compounds, and the compounds containing Dev.R demonstrated better properties than those containing GRP. © 2005 Wiley Periodicals, Inc.