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 UV-vis spectroscopy and transmission electron microscopy (TEM). The aqueous gold nanoparticle solutions were employed as catalysts in the reduction of p-nitrophenol and in the hydrogenation of cinnamaldehyde and were found to exhibit excellent activity under mild conditions.