An aluminum tungstate-scandium tungstate solid solution was successfully grown in a single crystal form by modified Czochralski (CZ) method. The crystal grown was transparent and a satisfactory quality was examined by a polarizing microscope measurement. The Al3+ ion conductivity was considerably improved by forming the solid solution and these by expanding the crystal lattice size. The lattice expansion contributes greatly to enhancing the Al3+ ion conducting behavior especially along c-axis among the three axes in the orthorhombic symmetry. By comparing the ion conducting characteristics between each axis of the single crystal and the polycrystal, the enhancement of the Al3+ ion conductivity is ascribed to the cooperative effects of both ion conductivity increase along c-axis and the conductivity enhancement in the grain boundaries.