Giant fibroadenoma is a rare disease with unknown etiology. During pregnancy, fibroadenomas increase in size and may show lactational histologic changes. High concentrations of estrogen, progesterone, and prolactin promote the ductal growth and formation of tubuloalveolar structures. This may be a reason for the significant enlargement in this period.We presented a case of giant fibroadenoma, first detected at the onset of pregnancy, which grew rapidly and was excised surgically two months after the birth. There was no marked deformity in the breast nor a need to reconstruct it, despite the giant mass was excised and the mother was lactating.We presented a rare case of giant fibroadenoma in a lactating woman. A progressively growing mass in breast can lead to structural damages. The current management approach for giant fibroadenomas is still surgical excision.