Chromosomes of interspecific hybrids of the Japanese wild Perilla (2n=20) were doubled by colchicine treatment to make their amphidiploids (2n=40), and their morphological characteristics and seed fertility were analyzed and compared with those of the parental wild species and their F_1 hybrids. Morphological characteristics of the F_1 plants were generally intermediate of those of their parental species. Flowers and bracts of the amphidiploids were one-and-a-half times bigger in size of those original F_1 plants but the shapes were alike. Leaf sizes of the amphidiploids were the same as those of the F_1 plants, but serrations were much bigger in the amphidiploids. Seed fertility rate was very low in the F_1 plants (0.5-10%) but was higher in the amphidiploids (16-70%), however, the rate recovery differed in degree among the strains.