Peritoneal pregnancy is an implantation in the peritoneal cavity exclusive of tubal, ovarian, or intra-ligamentary implantations. This is a rare obstetric complication with high maternal mortality and even higher perinatal mortality, and secondary type was most common. Risk factors for peritoneal pregnancy are previous history of extrauterine pregnancy or tubal surgery pelvic post-inflammatory status or presence of an intra-uterine device. As it is a life-threatening condition, expectant management carries a risk of sudden life-threatening intra-abdominal bleeding and a generally poor fetal prognosis. So, when it is recognized, immediate termination of pregnancy is usually recommended. Early diagnosis of peritoneal pregnancy is difficult, but is important by their life threatening progress course to patients. Recently, we experienced primary peritoneal pregnancy which meets both the original and modified criteria. In this paper, we reported the case of early diagnosed and successfully treated peritoneal pregnancy despite of their diagnosis was incidentally.