The experimental results on mechanical and thermal properties of composites of Al-powder filled cis-polyisoprene (CPI) and trans-polyisoprene (TPI) blends measured using dynamic mechanical analyser (DMA) and transient plane source (TPS) technique, respectively have been presented. Structural characterization of these composites has been done using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence (EDX). XRD measurements do not show the presence of Al-powder at its low concentration in the blend but the presence is confirmed at higher concentrations by the occurrence of corresponding peaks. Also increase in concentration of Al-powder increases crystallinity and crosslink density. Results on mechanical and thermal properties show that increase in concentration of AI-powder in the CPI/TPI blends increases glass transition temperature and improves the mechanical and thermal properties. This improvement in both properties of CPI/TPI blends due to incorporation of Al powder has been explained in terms of crystallinity and crosslink density. (C) 2012 Elsevier B.V. All rights reserved.