Abstract: Objective To explore the possibility of plasma miR-221 as a biomarker for chemosensitivity to neoadjuvant chemotherapy(NAC) in breast cancer patients. Methods The expression levels of circulating plasma miR-221 in 32 healthy individuals and 93 breast cancer patients who received NAC were assessed by QRT-PCR method. The correlation between miR-221 expression levels and clinicalpathological features and chemosensitivity were also analysed. Results miR-221 expression levels in the plasma of breast cancer patients(1.453±0.065) were significantly higher than those in healthy individuals (1.114±0.093)(P=0.007). miR-221 expression level was significantly associated with hormone receptor(HR) status (P=0.008). Patients with higher plasma miR-221 levels tended to be with HR-negative. Patients with different miR-221 levels had significant differences in overall response rate (ORR), not complete response (pCR) rate (ORR:P=0.044; pCR: P=0.477). Conclusion Plasma miR-221 expression may be a predictive biomarker for chemosensitivity to NAC in breast cancer patients.