The present study reports two cases of large ovarian malignancy during pregnancy, which is very rare. The two patients were received between Nov 2012 and Feb 2013 at Gynecological and Obstetrical Department, Women’s Hospital, School of Medicine, Zhejiang University (People’s Republic of China). Both cases present tumor sized more than 20 cm, with one case of 40 cm. Both patients underwent timely cesarean section, with survival of the Child, and successful removal of the tumor. All patients showed good outcome in the follow-up period. Therefore the large ovarian malignancy during pregnancy could be well treated after careful clinical evaluation.