The objective of this study was to investigate the clinical significance of real-time contrast-enhanced ultrasonography in the differential diagnosis of breast tumor. Fifty-seven breast tumor patients with 63 lesions were studied. Among the lesions, 34 are malignant and 29 are benign. A Philips iU-22 ultrasound scanner with L12-5 probe was used. Bolus SonoVue was injected via antecubital vein. Dynamic imaging was stored and analyzed with QLAB software. Parameters including initial time of perfusion (ITP), time to peak (TTP), peak intensity (PI), the enhancement pattern and the wash out pattern (WP) of contrast agent were observed. Results showed that about 85.3% of the malignant lesions showed heterogeneous enhancement and 79.3% of the benign ones showed homogeneous enhancement. The persistence time of the contrast agents was clearly longer inside the malignant lesion than inside the benign ones. Nevertheless, there were no significant differences in the value as ITP and TTP between the malignant and the benign lesions, while the PI value of the malignant lesions was significantly higher than the benign lesions. This study suggested that real-time contrast-enhanced ultrasonography is helpful to the differential diagnosis of breast tumors; however, the WP of the contrast agent inside the lesion also seems to be an important factor.