A direct method of determination of the valence-electron structure from its crystal structure has been presented by the writer at XIIth International Congress of Crystallography, at Ottawa, 1981. Here the method is applied to determine the valence-electron struc-tures of Y3Aℓ5012 (YAG) and Ak203, Cr203 (ruby) to see how certain properties of these laser materials are related to their valence-electron structures. The first point observed is the very strong, continuous, but zig-zag three-dimensional fractional covalent M-0 bond nets (M = Ak or Cr) being connected with the high melting points, the great resistance against the puncture by the strong laser beam. In the case of Nd-YAG, the distortion caused by the replacement of the Y atoms by almost the same size Nd atoms is small. On the other hand, because of the similarity of the valence-electron structures of oc-AZ203 and Cr203, the replacement of Ak atoms by the little larger size Cr atoms in small amount is easily understood. The large atomic spins of magnetic moment mg = 2.76 μb (= experiment value, the theoretical mB = 2.702 μg) of Cr atoms pointing paralell to the c axis of the hexagonal lattice, is found to be due to the direction of the spin situated in the space of lowest density space of the valence-electron cloud distribution. This agrees with the result of a-Fe disclosed in the paper "Electron theory of the magnetic moment structures of a-Fe, 6-Co, Ni from neutron diffraction experiments" presented at the Symposium on Neutron Scattering, Argonne National Laboratory, 1981. This will be found also true in many other oxides like a-Fe2O3, FeTiO3, MnTiO3 and so on.'