Blends of ethylene-propylene-diene monomer (EPDM) and polyaniline (PAni) doped with dodecylbenzene sulfonic acid were prepared by mechanical mixing in an internal mixer at various compositions and times. Reflectivity characteristics of the blends in the 8-12-GHz range were investigated with the Naval Research Laboratory arch method. The microwave absorption behavior was affected by the processing time and blend composition. The correlation of reflectivity measurements with morphology observations made with scanning electron microscopy suggested that the distribution and concentration of the PAni phase within the EPDM matrix altered the wave-matter interactions. The radar-absorbing materials prepared in this work showed broadband behavior with microwave radiation absorption of up to 90%. (C) 2002 John Wiley & Sons, Inc. J Appl Polym Sci 83: 1568-1575, 2002.