In order to screen mulberry genotypes suitable for fruit production, fruit traits of 260 genotypes were examined. Forty-three genotypes were classified into staminate, 137 were pistillate and 78 were hermaphrodite. Fruit quantity and size showed wide variations among the genotypes. Itouwase, Shizensei-roso and Tenmokuyotsume bore more fruits than the other genotypes. Okaraguwa bore the largest fruits, which were 4.9 cm long and weighed 7.15 g. The sugar content of the fruit ranged from 6.6 to 20.8%, and the highest content was observed in Myurienoaaru. Most of the taste panelists rated Okaraguwa and Kataneo higher than the other genotypes. Thus, these 2 genotypes were selected as the most suitable for fruit production. In the next step, we attempted to develop polyploids from these genotypes by colchicine treatment to achieve a high productivity. After the treatment, we propagated the shoots with putative tetraploids to obtain the strains. The 2 strains thus developed were mixoploids of diploids and tetraploids, but it is considered that they were both peripheral chimeras and that their structure remained stable. One of the strains, FRM-01 developed from Kataneo, bore many fruits in the second year after planting in the field. Almost all the fruit traits of this strain were the same as those of the original strain, except that the size became larger and the fruit yield was increased by about 60%.