A localized molecular orbital treatment based on an anion coordination octahedron model has been extended to a systematic calculation on the refractive indices of crystals (9 in all) of the perovskite and the tungsten bronze structure types (without in-troducing any adjustable parameters.) It is found that agreement with experimental data is fairly satisfactory while the deviation is ca. 10 percent. As a straightforward ccnsequence to these calculations, we have been able to elucidate the mechanism of the electro-optical and the non-linear optical effects in crystals of these two structure types and give a good estimate of various properties associated with the linear optical susceptibilities within the range of optical frequencies. In addition, it is shown that although the odd-ordered term drystal field is the decisive factor in the electro-optical and the non-linear optical effects, its contribution to the linear optical susceptibilities is, however, rather small. Finally, a brief discussion is made as to the feasibility of the localized molecular orbital method in the treatment of certain problems in the theory of solid state physics.