After mullite fibers particles (MFPs) were surface modified, conductive polypyrrole (PPy) layer was chemically grafted on the surface of the self-assembled monolayer (SAM) coated MFPs, via in situ surface-initiated polymerization, resulting in SAM-MFPs/PPy composites. The composites possess high electrical conductivity at room temperature, weakly temperature dependence of the conductivity. The nanocomposite electrochemical properties displayed nearly symmetric charge–discharge characteristics and an ideal rectangular cyclic voltammogram. X-ray diffraction analysis confirmed that the main peaks of SAM-MFPs/PPy composites are similar to the SAM-MFPs, which reveal that the crystal structure of SAM-MFPs is well-maintained after the coating process under polymerization reaction conditions and exhibit semicrystalline behavior. Thermogravimetric analysis shows that the thermal stability of SAM-MFPs/PPy composites was enhanced and these can be attributed to the retardation effect of amine functionalized MFPs as barriers for the degradation of PPy. The morphology of SAM-MFPs/PPy composites showed the coaxial fibrous structure. POLYM. COMPOS., 35:892–899, 2014. © 2013 Society of Plastics Engineers