Abstract: ［Abstract］Objective　To assess the value of diffusion weighted imaging（DWI） in monitoring therapy effect of neoadjuvant chemotherapy（NAC）in patients with locally advanced breast cancer. Methods　The prospective study included 26 lesions in 24 patients with LABC undergoing NAC．MRI was conducted before chemotherapy，after the first cycle of chemotherapyand after all cycles，including conventional MRI and DWI．All patients were confirmed by pre-treatment fine needle aspiration biopsy（FNAB），and postoperative histopathological prout. All lesions were divided into two groups of pathological complete response（pCR）and non-pCR. We evaluated ADC value and its changes in pathological complete response difference between the groups and complete remission in each testing point．Results　Before chemotherapy and after the first cycle of chemotherapy，the ADCmean and ADCmin had no statistically significant difference hetween pathologic complete response group and non-complete remission．After the whole chemotherapy，both of them had statistically significant difference;pathological complete response（pCR）and non-pCR early ADCmin value rate were（16.78±22.70）% and （12.37±10.09）% respectively．No statistically significant difference was seen（P = 0.53）. Preoperative ADCmin value rates were（91.41±45.83）% and（29.74±22.96）% respectively，which were statistically significant（P = 0.00）．Conclusion　ADC which is measured from DWI can be used to assess early response to NAC in breast cancer lesion， but cannat predict pCR or non-pCR for all cycles of chemotherapy on the first cycle.