Melting of slush ice in a horizontal cylindrical capsule has been investigated experimentally to determine the interaction of fluid flow induced by both motion of the slush ice and free convection owing to thermal and concentration diffusion. The slush ice, which is a mixture of fine ice particles and ethylene glycol aqueous solution, was utilized as a testing material and was heated by the capsule wall. During the melting process the slush ice is drawn by buoyancy to the top of the heated capsule where close-contact melting occurs. Melting behavior and melting rate of the slush ice were observed and measured for parameters such as initial concentration of aqueous binary solution and heat flux. The results revealed that the melting heat transfer of slush ice is markedly effected by free convection in the double-diffusive layers arose from the thermal and solutal buoyancy forces.