Gold nanoparticles were prepared in an aqueous solution and a 50:50 N-methyl-2-pyrrolidone (NMPD)/toluene mixed solvent using o-anisidine as the reducing agent, respectively. The reaction is conducted by choice of the temperature and medium. Transmission electron microscopy (TEM) and UV−vis absorption spectroscopy measurements show that the size of Au particles is dependent on the synthetic protocols. At the same time, the oxidative polymerization of o-anisidine was achieved. Moreover, the structure of the polymer varied with the preparative conditions. Cross-linked poly(o-anisidine) and poly(o-anisidine) in its doping state (in the form of the emeraldine salt) were obtained, respectively, supported by UV−vis absorption spectra, infrared spectra, and X-ray photoelectron spectroscopy (XPS).