We present a case of alveolar soft part sarcoma (ASPS) of the pectoris major muscle in a 20-year-old female. She felt a mass in her right side breast for 7 years. The lesion was almost the same size with occasional throbbing pain and tenderness. Fine needle aspiration of the tumor was performed in the OPD and suspicious abnormal cells were reported. Ultrasound (US) examination of the breast revealed a large heterogeneously hypoechoic lesion contiguous to the pectoris major muscle. Profound color flow signals were evident in both central and peripheral regions of the mass. Spectral Doppler US showed high flow velocity in the tumor vessels with resistivity index of 0.73. Surgical intervention was performed and the histological examination yielded a diagnosis of ASPS.