Abstract High quality microspheres self-assembled from nanowires of polyaniline (PANI) are prepared by a self-assembly process using ammonium peroxydisulfate as oxidant in aqueous solution. The microspheres of about 2.6 μm average diameter are composed of uniform nanowires with 40–60 nm in diameter. The formation process of PANI microsphere indicates that its evolution of morphologies can be divided into three stages. First, a large quantity of PANI nanowires form, then porous microspheres develop, and finally most of nanowires transform into microspheres. The morphology and uniformity of the PANI microspheres mainly depend on the mole ratio of aniline to ammonium peroxydisulfate. The BET specific surface area and conductivity of the polyaniline porous microsphere at room temperature are 53 m 2 g − 1 and 3.3 × 10 −1 S cm − 1 , respectively.