The differential molar adsorption enthalpy of radon at zero coverage on the surface of laboratory made ice was determined by the method of low-temperature thermochromatography. Spherical ice particles were prepared as the stationary phase. For the investigation, the short-lived radon isotope Rn-220 was used, generated with a U-232-emanation source. Helium served as carrier gas. At a temperature of about 100 K, sharp adsorption peaks of the Rn-220 atoms (similar to 10(8)) were measured. From the measured deposition temperatures the adsorption enthalpy on the surface of the ice spheres was determined as Delta H-ads = -19.2 +/- 1.6 kJ/mol. This value is compared with data from the literature for adsorption enthalpies of radon on different solid surfaces. From the estimated solution enthalpy of radon in water and the formation enthalpy of a hypothetical "Rn chlathrate hydrate", it follows that Rn is adsorbed on the ice surface as a free atom. The measured adsorption enthalpy indicates that Rn and ice are not isomorphous and that Rn shows no solubility in the solid phase.