This study was carried out to examine the spectral properties of the red fluorescence emitted from oral squamous cell carcinoma (SCC). Fluorescent samples obtained from oral cancers induced in hamsters, human oral SCCs, and the medium from cultured oral cancer cell lines were analyzed with a spectrofluorometer with excitation at 404 nm. The spectral profile of the experimentally induced cancers changed with increasing malignancy: peaks at 634 and 672 nm increased and peaks at 520 and 582 nm decreased. A reduction in fluorescence intensity at 582 nm and a rise of intensity at 634 nm were commonly observed in the experimental, clinical, and cell line samples, and the ratio of the fluorescence intensity at 582 nm over that at 634 nm was consistent in all samples. These results suggested that the red fluorescence was emitted by porphyrin, which we believe to be produced by oral SCCs and to accumulate inside or on the surface of cancer tissues in greater amounts with progressing malignancy.