Ultraviolet absorption spectra and fluorescence spectra of many derivatives of benzene and naphthalene heterocyclic N-oxides and a few derivatives of anthracene and phenanthrene heterocyclic N-oxides were recorded in various solvents. Experimental results were discussed from the point of solvent effect and substituting effect. Ultraviolet spectra of all N-oxides used showed increasing blue shift with increasing polarity of the solvent. These results agreed well wlth the behavior in the solvent effect which was reported in previous papers for basic heterocyclic N-oxides and their simple derivatives. It is suggested that this solvent effect is a general property for heterocyclic N-oxides. As for the fluorescence spectra of N-oxides, such a general property as was observed on ultraviolet spectra was not observed. A main reason for this solvent effect is attributed to hydrogen bonding such as ⪖N→O⪖H (in solvent). On the other hand, a relationship was found to exist between the effect of substituting positions and the spectra. By arranging many substituents in the order of substituting ability and classifying the positions in a molecule belonging to two ring systems into two classes, it has been found that the above relationship is present between ¹L_b and ¹L_a absorption bands. This property may also be considered as a general property.