Spherical nickel oxide (NiO) nanoparticles were prepared by using nickel chloride as precursor in the ethylene glycol as solvent and urea as precipitant. The X-ray diffraction study showed that NiO has single-phase cubic structure with average crystallite size of 35 nm. The prepared NiO nanoparticles were incorporated into polyaniline (PANI) matrix during in situ chemical oxidative polymerization of aniline with different molar ratios of aniline: NiO (12 : 1, 6 : 1, and 3 : 1) at 5 degrees C using (NH(4))(2)S(2)O(8) as oxidant in aqueous solution of sodium dodecylbenzene sulfonic acid, as surfactant and dopant under N(2) atmosphere. The synthesized composites have been characterized by means of X-ray diffraction (XRD), thermogravimetric analysis, Fourier transform infrared (FTIR), scanning electron microscopy, TEM, and vibrating sample magnetometer for its structural, thermal, morphological, and magnetic investigation. The XRD and FTIR studies show that the NiO particles are in the composite. The room temperature conductivities of the synthesized PANI, PANI/NiO (12 : 1), (6 : 1), and (3 : 1) composites were found to be 3.26 x 10(-4), 1.88 x 10(-4), 1.5 x 10(-4), and 4.61 x 10(-4) S/cm, respectively. The coercivity (H(c)) and remnant magnetization (M(r)) of NiO, PANI/NiO NC(s) (12 : 1), (6 : 1), and (3 : 1) at 5 K was found to be 8.22 x 10(-2), 6.31 x 10(-2), 6.42 x 10(-2), 6.27 x 10(-2) T, and 6.64 x 10(-3), 1.83 x 10(-4), 3.07 x 10(-4), and 3.98 x 10(-4) emu/g, respectively. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1905-1912, 2011