The world tendency toward using recycled materials demands new products from vegetable resources and waste polymers. In this work, composites made from powdered tire rubber (average particle size: 320 mum) and sisal fiber were prepared by hot-press molding and investigated by means of dynamic mechanical thermal analysis and tensile properties. The effects of fiber length and content, chemical treatments, and temperature on dynamic mechanical and tensile properties of such composites were studied. The results showed that mercerization/acetylation treatment of the fibers improves composite performance. Under the conditions investigated the optimum fiber length obtained for the tire rubber matrix was 10 mm. Storage and loss moduli both increased with increasing fiber content. The results of this study are encouraging, demonstrating that the use of tire rubber and sisal fiber in composites offers promising potential for nonstructural applications. (C) 2003 Wiley Periodicals, Inc.