Three indigenous mulberry species of Morus tiliaefolia Makino, Morus mongolica C. K. Shneider and Morus bombycis Koidz. were naturally crossed and their fertilities and fruit characteristics were investigated during the years of 1996 and 1997. M. tiliaefolia Makino and M. mongolica C.K. Schneider showed low fertility, but M. bombycis Koidz. was medium in fertility. The fruits of M. tiliaefolia Makino were red-purple and midium in size and high sugar content, but those of M. mongolica C.K. Schneider were light red and small but extremely high sugar content. The total acidity of fruits was 0.73, 0.50 and 0.36-0.94% in M. tiliaefolia Makino, M. mongolica C.K. Schneider and M. bombycis Koidz. respectively. Regarding ripenening stage, M. mongolica C.K. Schneider was early and M. tiliaefolia Makino was medium, while M. bombycis Koidz was early or medium.