The effect of conductive polymer matrix including polyaniline (PANI) and polypyrrole (PPy) on the magnetoresistance (MR) behaviors in the variable range hopping (VRH) regime has been investigated in the disordered polymer nanocomposites containing tungsten trioxide (WO3) nanoparticles. These nanocomposites have demonstrated ultrahigh MR sensitivity at low magnetic field regime. The observed positive MR has been well explained by the wave-function shrinkage model. The conductive polymer matrix has shown different effects on the MR behaviors of the nanocomposites. The WO3/PANI nanocomposites have a lower localization length (a(0)) and density of states at the Fermi level (N(E-F)), and higher average hopping distance (R-hop) and average hopping energy (W) compared with those of the WO3/PPy nanocomposites. (C) 2013 Elsevier Ltd. All rights reserved.