Two cases of rudimentary uterine horn were able to be diagnosed prior to operation. The case of rudimentary horn with cavity non-communicating to unicornuate uterus was easy to diagnose. Transabdominal ultrasonography and computed tomography (CT) demonstrated the uterus to have binodular structure and two uterine lumina. However, the case with pregnancy was difficult to diagnose. In this case, thick myometrium could be seen by ultrasonography to enclose the sac. In both cases hysterosalpingography revealed unicornuate uterus.