Burkitt's lymphoma of the breast is a rare kind of malignancy, which usually occurs among women during pregnancy or breastfeeding. A rapid diffuse swelling of bilateral breasts is the most common mode of presentation. This article reports a rare case of Burkitt's lymphoma of the breast during pregnancy. The patient presented with diffuse enlargement of both breasts with skin erythema, and increased skin temperature, which brought difficulty in distinguishing it from inflammatory breast cancer and gestational mastitis. The rare clinical manifestations pose a challenge for early diagnosis, only by a series of imaging tests. Until the fine needle aspiration of breast revealed lymphoma cells and a subsequent bone marrow biopsy revealed a translocation of chromosome No.8 and No.14, the final diagnosis was ensured. Meanwhile, imaging examination indicated a huge retroperitoneal mass at a maximum diameter about 10 centimetre. It was significantly reduced together with breast lesion during the standardized chemotherapy. For a rapid progression and poor prognosis, an early diagnosis and prompt therapy are especially important for this very disease. This article provides a patient with an atypical presentation accompanied by a massive retroperitoneal neoplasm, to alert clinicians and help them learn more about this rare disease.