OBJECTIVE To evaluate the clinical significance of preoperative ultrasound diagnosis and classification of ovarian pregnancy (OP). METHODS The ultrasonographic reports, medical records, and operative summaries were reviewed for twelve women with a confirmed diagnosis of OP. According to the ultrasonographic appearance, OP was classified into two types. For every type, we analyzed the possibility and clinical significance of preoperative ultrasound diagnosis, combining with its clinical manifestations and treatments. RESULTS According to sonographic features, twelve cases of OP can be classified into ruptured type (n = 6) and unruptured type (n = 6), the latter was subclassified into embryo sac type (n = 2) and non-homogeneous mass type (n = 4). All the unruptured OP have the characteristic solid hyperechoic rings or masses, and 66.7% (4/6) were correctvly diagnosed by preoperative ultrasound. No characteristic ultrasonogram was detected in ruptured OP which were all diagnosed as ruptured ectopic pregnancy (EP) or corpus luteum by preoperative ultrasound. The diagnostic and surgical procedures of four cases diagnosed by preoperative ultrasound were all laparoscopy and removal of the gestational products, and their average hemoperitoneum, operation time, hospital days was 313 ± 278 ml, 57 ± 9 min, and 4.25 ± 0.5days, respectively. While ruptured OP cases (6 cases diagnosed at first visit and 1 underdiagnosed but ruptured after 6 days), the diagnostic procedures was laparoscopy(3/7) or laparotomy(4/7), the surgical procedure was removal of the gestational products(2/7), wedge resection(3/7), or adenexectomy(2/7), and their average hemoperitoneum, operation time, and hospital days was 1914 ± 1059 ml, 93 ± 17 min, and 5.9 ± 1.3days, respectively. CONCLUSIONS Ultrasound plays a significant role in diagnosis of OP, and part of the unruptured OP based on the typical sonographic characteristics could be correctly diagnosed by an experienced sonographer, this is beneficial and effective in terms of the risk of patient's operation and life. Whereas ruptured OP were generally diagnosed as ruptured EP or corpus luteum because there were no characteristic ultrasound manifestations.