Uniform double-shelled polystyrene/poly(o-toluidine) (PS/POT) composite hollow spheres with tunable shell thickness of the POT layer have been successfully synthesized by a simple method. POT was directly coated onto the surface of negatively charged PS template spheres, which were synthesized by soap-free emulsion polymerization. Surprisingly, the resultant spheres show a double-shelled hollow structure with PS as an inner wall and POT as an exterior shell. In comparison to conventional methods, the benefits of this route are that neither organic solvents nor high-temperature calcinations were used to remove the PS template. The surface morphology, the shell thickness, and the compositions of the double-shelled spheres were systematically characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. On the basis of our interpretation of experimental results, a mechanism for the formation of the double-shelled PS/POT, composite hollow spheres is proposed.