This research was focused on the mechanical properties of electrically conducting composites based on polyaniline (PAn)-coated short glass fibers (SGFs) immersed in an isotactic polypropylene (iPP) matrix. In these composites, PAn was actually grafted onto the SGF surface, and so it was denoted PAn-g-SGE The tensile, flexural, and interlaminar fracture toughness was investigated. To study the influence of PAn-g-SGF, three different concentrations (10, 20, and 30 wt %) were melt-mixed in the iPP resin with a batch mixer. X-ray patterns of the as-molded plaques of iPP and its composites showed an isotropic orientation. Uniaxial tensile deformation revealed that the Young's modulus and tensile stress increased as the concentration of PAn-g-SGF increased, on the other hand, the strain at failure was significantly reduced (by 2 orders of magnitude) with respect to the neat iPP. Scanning electron microscopy studies on the failure specimens indicated that the significant reduction of the strain at failure was due to the low interfacial bonding between the fibers and the surrounding matrix. Moreover, X-ray scattering analyses of the fractured regions showed that the uniaxial deformation enabled significant molecular orientation in the iPP, whereas the fractured composites remained isotropic. Detailed scanning electron microscopy analyses showed that the fracture mechanism arose from the fracture of the PAn-g-SGFs; the percolated PAn-g-SGFs formed a path for the stress transfer. Because the failure was dominated by both filler decohesion and polymeric chain rupture, the strength was not influenced significantly by the amount of PAn-g-SGFs. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 934-941, 2009