A new water-soluble methyl-imidazolium-based ionic polymer was synthesized by ring-opening metathesis polymerization that was subsequently used to prepare aqueous gold nanoparticle solutions which were characterized by UVvis spectroscopy and transmission electron microscopy (TEM). The aqueous gold nanoparticle solutions were employed as catalysts in the reduction of pnitrophenol and in the hydrogenation of cinnamaldehyde and were found to exhibit excellent activity under mild conditions.