Chromosome number, meiotic behavior, genomic in site hybridizatio, enzyme electrophoretic studies were made on Japanese Polystichum. Polystichum Polyblepharum (Room. ex kunze) Pr., P.longifrons kurata, P.tagawanum Kurata, P.pseudo-makinoi Tagawa, P.ovatopaleacum (Kodama) Kurata, and P.makinoi (Tagawa) Tagawa were tetrads with 2n=164. Many of them displayd 82 bivalents in metaphase I,and reproduced sexually. Polystichum kiusiuensis Tagawa, P.eximium (Mett.Ex Kuhn) C.Chr. P.otomasui Sa.Kurata and P.fibrilloso-paleaceum (Kodama) Tagawa were diploids with 2n=82. In meiotic metaphase I,41 bivalents were formed in P.eximium and P.fibrilloso-paleaceum. All of putative hybrids P.*anceps Kurata, P.*hakonense kurata, P.*hatajukuense Kurata, P.*kiyozumianum Kurata, P.*pseudo-ovatopaleaceum Akasawa and P.*takaosanense Kurata were tetraploids with 2n=164 and their meiosis were irregular. Allozyme variations of sexual tetraploids displayd typical allopolyploidal patterns. Heterozygotic bands of sporophytes did not segregate in gametophyes, and they were fixed heterozygosity. Hybridities of putative hybrids were confirmed by their allozyme patterns. Genetic identity values between tetraploid species were high, while those values between diploids and tetraploids were low. GISH also confirmed genetic differences between diploid and tetraploid species.