We report the thermal conductivity and the Seebeck coefficient of polycrystalline samples of Cu6O8YCl1-xBrx. The lattice constant a linearly increases with increasing Br- concentration x, indicating an expansion of the Cu6O8 cage. At 350 K, the thermal conductivity κ is small and undergoes very little change with x, suggesting the existence of an anharmonic vibration. On the other hand, the Seebeck coefficient S is enhanced by substituting Br- for Cl-. These facts indicate that the thermoelectronic properties are sensitive to the Cu6O8 cage size in the Cu6O8YCl system. © 2013 The Korean Physical Society.