To see the distribution of ferns in the southern part of Japan Proper, I take up the following four districts: The Island of Sikoku, Kii Peninsula, Idzu Peninsula, Boso Peninsula. The coastal fern flora of these four districts is rich of Malayan and South Chinese elements. The frigid elements are seen only in the alpine region of Sikoku. Numerous species are common with Corea, Shantung and Central-China. Endemic plants are very rich. Their distribution agrees with that of Phanerogams. Temperature is the principal factor of controlling the distribution, but geology has almost no consequence. Humidity gives a slightest influence, for it is being similar in those districts.