The objective of this study is to develop microwave absorbers using both dielectric and magnetic lossy materials. Polypyrrole (PPY) is used as dielectric lossy materials and carbonyl iron particles is used as magnetic lossy materials. Polypyrrole powders are prepared by in situ polymerization method. Then PPY-carbonyl iron composite with different mixture ratios have been prepared by as-prepared material. The structure, morphology and properties of the composites are characterized with IR, XRD, scanning electron microscope (SEM), Net-work Anlyzer. The complex permittivity (epsilon(r)' - j epsilon(r)'') and reflection loss (dB) of the composites have been measured at different microwave frequencies in S-band and C-band (30-6000 MHz) employing vector network analyzer model HP 8722ET vector. The effect of the mass ratio of PPY-carbonyl iron on the microwave loss properties of the composites is investigated. A possible microwave absorbing mechanism of PPY-carbonyl iron composite has been proposed. The PPY-carbonyl iron composite can find applications in suppression of electromagnetic interference (EMI), and reduction of radar signature. (C) 2011 Elsevier B.V. All rights reserved.