Ectopic breast tissue, or supernumerary breast tissue, is a rare congenital anomaly that can occur along the milk line, extending from the axilla to the groin. Ectopic breast tissue can undergo the same changes as normal breast tissue, including hormonal changes during pregnancy and lactation, as well as the development of benign or malignant tumors. Herein, we present a case of ectopic breast tissue presenting as axillary masses in a young woman. The patient was a 32-year-old woman who presented with two axillary masses that appeared during lactation after her first and second pregnancies, and now had reappeared. The masses had the consistency of breast tissue and were confirmed as supernumerary bilateral breasts on echomamography. Although supernumerary breasts are usually benign and asymptomatic, they can sometimes become cancerous. Therefore, surgical excision is often recommended, particularly in cases where the mass is symptomatic or growing rapidly.