Metallic polypyrrole with the conductivity of 4700 S/m has been synthesized by in situ polymerizing pyrrole in the aqueous solutions into which a specific amount of 9,10-anthraquinone-2-sulfonic acid sodium salt was dissolved. The effects of the salt 9,10-anthraquinone-2-sulfonic acid sodium on the conductivity of the polypyrrole have been investigated with the techniques of thermal gravimetric analysis, differential thermal analysis, and laser light scattering, respectively. The sizes of the resulted polymeric particles indicate that the addition of the salt can dramatically affect the chain length of the synthesized polymer. Our results have demonstrated that the salt-induced increase in the conductivity is closely correlated to the salt-induced increase in the chain length of the polymer.