Malignant phylloides tumor is a relatively rare and rapidly growing tumor of the breast. Presentation during pregnancy is uncommon. Reports regarding malignancy in these tumors differ greatly in incidence, and most of them are stromal malignancies. We report this case in which 24-year old primigravid patient in the 36th week of her pregnancy had a malignant phylloides tumor of breast with sudden growth and fine needle aspiration cytology of the breast was positive for malignancy. Ultimately after her caesarean delivery, excision biopsy was in favor of a malignant process. Pregnancy with nulliparous prolapse is also a rare condition. Those conditions are not associated with each other, but presence of two rare conditions in the same time in the same person is unique.