Provided are polyaniline coordinated with a transition metal, a core-shell nanoparticle including the same as a core, and preparation methods thereof. According to the polyaniline coordinated with a transition metal and the nanoparticle of the present application, it is possible to prepare polyaniline coordinated with a transition metal using an oxidizing agent having a core-shell structure and including the transition metal and a nanoparticle including the same as a core. The polyaniline prepared as such is in a doped state, and, thus, a preparation process is simple. Further, dispersibility with respect to a solvent is improved, and a band gap level of the polyaniline can be easily regulated.