Raman spectra of uranyl ion-loaded silver and gold colloidal particles have been measured. The Raman active symmetric stretching frequency of uranyl ions shifts to a smaller wavenumber by the adsorption onto silver and gold sols. The shift is so large that it discounts the case of weak bonding between uranyl species and both sols and suggests extensive sigma donation from the surface of the sols to the equatorial plane of the adsorbed uranyl species. For the silver sols, the Raman spectrum changes significantly upon varying the pH of the colloidal suspensions and corresponds to different adsorbed species. For the gold sols, the Raman spectrum does not change upon varying the pH and thus corresponds to only one adsorbed species. The notion that adsorption of uranyl ions involves the release of ligands was confirmed for gold sols but discounted for silver sols.