A putative hybrid of the fern genus Pteris was collected on Okinawa Island. It was morphologically intermediate between P. ryukyuensis (section Pteris) and P. semipinnata (section Campteria), suggesting that it might be an intersectional hybrid between them. The hybrid nature of the plant also suspected because of the abnormal morphology of the spores and sporangia. To clarify the parcentage of this putative hybrid, we analyzed the nuclear (nDNA) and chloroplast (cpDNA) DNA of all three of them. PCR analysis of the internal transcribed spacer 1 region of the nDNA indicated that the putative hybrid possessed nDNA of P. ryukyuensis. Furthermore, PCR-SSCP analysis of the intergenic spacer between psbC and trnS of cpDNA showed the putative hybrid to have the same electrophoretic pattern as P. semipinnata. Because the cpDNA is generally maternally inherited, we concluded that the putative hybrid was an intersectional hybrid between P. ryukyuensis and P. semipinnata, with the latter species functioning as the mother.