Cornual pregnancy is uncommon among ectopic pregnancies. A diagnosis of cornual pregnancy remains challenging, and rupture of a cornual pregnancy causes catastrophic consequence due to massive bleeding. We report a case of a ruptured cornual pregnancy occurring at 12 weeks of gestation. A 34-year-old woman was suspected of having a left cornual pregnancy at 11 weeks of gestation. Transabdominal ultrasound and magnetic resonance imaging revealed an eccentric localization of a gestational sac containing a viable fetus outside the uterine cavity adjacent to the left uterine cornua. The gestational sac was surrounded with a thin myometrial layer. The patient developed a rupture of the left cornual pregnancy with unstable hemodynamics. She underwent emergency laparotomy, which revealed the ruptured left cornual pregnancy with a hemoperitoneum. Cornual resection was performed. The pathological examination confirmed a ruptured cornual pregnancy.