A new polymer nanocomposites of an epoxy resin matrix with randomly dispersed nano-vanadium sesquioxides (V2O3) in various amounts were prepared. The structure of the nanocomposites were characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction, hardness, packing factor, extent of filler reinforcement, glass transition temperature, and sound velocity. The percolation threshold in the conductivity of the composites is lesser than 8 wt % and the dielectric constant can reach as high as 103. The resistivity-temperature curve of the composites shows a positive temperature coefficient (PTC) effect. The thermal stability of the composites was examined in terms of thermal gravimetry and differential scanning calorimetry (TG and DTA) and isothermal resistivity-time check. Because of the interfacial interaction among filler particles and the epoxy matrix, the nanocomposites exhibit higher thermal stability. The current-voltage-temperature curves behave as switching current. The temperature increases linearly with the applied voltage which makes this PTC nanocomposites very useful for temperature probe. Finally, electromagnetic interference shielding effectiveness (SE) values have been calculated and measured for the nanocomposites in the frequency range 1-12 GHz. It is found that the SE properties of the nanocomposite improve with increase in wt of V2O3. A maximum SE of 42 dB for V20 sample at 12 GHz has been achieved. These nanocomposites are potentially useful in suppression of electromagnetic interference and reduction of radar signature. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 817-825, 2010