The synthesis of polyaniline (PANI) nanospheres by a simple template-free method has been described. The polymerization of aniline in aqueous medium was accomplished using ammonium persulfate without any protonic acid. The UV-vis spectrum of PANI nanospheres displayed the characteristic absorption peak of π-π* transition of the benzenoid ring at 355 nm. The oxidation state of PANI nanospheres was identified with FT-IR spectroscopy by comparing the two bands at 1582 (ring stretching in quinoid unit) and 1498 cm(-1) (ring stretching in bezenoid unit). The X-ray diffraction patterns demonstrated the low crystalline nature of PANI nanospheres. The morphology of PANI nanospheres was spherical and the mean diameter of nanospheres was found in the range of 3-12 nm. The thermal behavior of PANI nanospheres was studied by thermogravimetric analysis. The effect of doping of HCl and H(2)SO(4) on PANI nanospheres was studied by measuring the current as a function of time of exposure. The high electrical conductivity of 6×10(-2) S cm(-1) was obtained for PANI nanospheres at their optimum doping state by 100 ppm HCl.