Various types of single crystals for the aluminum tungstate-scandium tungstate solid solutions were successfully grown by modified Czochralski (CZ) method. The crystals grown were transparent and a satisfactory quality was identified by a polarizing microscope measurement. Both Al and Sc elements were clearly found to exist by electron probe microanalysis (EPMA) measurements and the single crystals grown were clarified to be exactly the solid solutions by the X-ray powder diffraction analysis. The Al : Sc ratio in the single crystal solid solutions was precisely determined from the lattice parameters obtained by the X-ray powder diffraction analysis. The Vickers hardness of the single crystals was also determined and it was clarified that the hardness of the crystal bulk was monotonically reduced with the increase of the Sc content in the solution, because larger Sc3+ ions microscopically expanded the neighboring layer in the layered Sc-2(WO4)(3)-type structure due to their larger ionic size compared with that of Al3+ and the expansion resulted ill an incommensurate layered structure.