Objective To investigate the value of apparent diffusion coefficient (ADC) of diffusion-weighted magnetic resonance imaging (DW-MRI) in patients wtih breast benign lesions Methods 109 patients, 115 benign lesions,41 fibroadenoma,28 cysts,26 adenosis,5 mastitis,2 intraductal papillomas，2 hamartomas, 2 tuberculosis，9 lipoma. All cases were pathologically confirmed.All patients were scan with 3 b values (b=400-0,800-0,1000-0s/mm 2) in DWI.Then the ADC value and the area of and the singnal intensity and the findings of lesions in DWI were calculated.Results All lesions have significant differences between the ADC values of fibroadenomas, cysts, ndenosis,as well as mastitis and normal breast tissue respectively;There were significant differences between the ADC values of cystic diseases and non- cystic lesions; There were no significant differences among the ADC values of fibroadenoma, ndenosis and mastitis.There were no differences among ADC values in cystic diseases during 3 b value .But there were significant differences among ADC values in non- cystic diseases during 3 b value. And the lower the b value,the higher the ADC;The singal intensity and area of the most of benign lump are decrease with the b valuec increasing. Except 9 lipomas ,all the benign lesions manifest hyper-singnal intensity or iso-singnal intensity or mixture intesity. Conclusion ADC value may help to differentiate cystic diseases and non- cystic diseases; The signal intensity and area of benign lump in DWI show discrepant regularity with b value increasing. It can be used to differenciate diagnosis.