A comparison of spectra of uranylions in HCl- and dioxane-solutions leads to the conclusion, that dioxane increases complex formation. The investigation of these spectra has shown the occurance 'of two complex equilibria regarding the formation of chlorocomplexes beside any hydrolytic effects. The formation constants were determined. Measurements of conductance confirm the spectrophotometric derived equilibria. The replacement of water by dioxane in the inner solvation sphere, of uranylions can be excluded up to about 60% dioxane.