Recently, polyaniline has been focused increasingly due to its unique optical and conductive property. However, its poor stability and uncontrolled morphology greatly limited  its further application. Herein, polystyrene sulfonic acid (PSS) was used as a template for in situ polymerization of aniline to fabricate stable polyaniline nanomaterials, in which ferric chloride and ammonium thiosulphate were employed as the oxidants, respectively. The selfassembled morphology and the optical property of the resultant aggregates were examined by electron microscopy and ultravioletvisible absorption spectroscopy. The selection of oxidants had great effects on the morphology of polyaniline, and spherical nanoparticles with uniform size and regularity were obtained for ferric chloride, and elongated nanofibers of polyaniline were observed from the oxidation of ammonium thiosulfate. The fabricated polyaniline nanoparticles possessed significant photothermal effect, which is promising in tumor photothermal therapy.