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The characteristics of the fluorescence spectra of polyethylene 2,6-naphthalate (PEN) films were compared with those of poly(ethylene terephthalate) (PET). The fluorescence spectra of PEN films were found, by photoselection, to consist of two components, one peaking at 425 nm and the other at 445 nm, with their emission transition moments perpendicular to each other. The integrated excitation spectra of the PEN films were much more intense than those of PET. After the resolution of the integrated excitation spectra of PEN, most, but not all, of their component peaks corresponded to those of the absorption spectra. On the basis of this fact together with previous data on photodegradation, the spectral component peaking at 445 nm originated, at least partly, from traces of photochemical products generated by exposure during the measurements.