Objective To investigate the correlation between the characteristics of peritumoral edema and the aggressiveness of breast invasive ductal carcinoma in preoperative magnetic resonance imaging(MRI).Methods A total of 79 patients(79 lesions)who underwent radical mastectomy in the First Affiliated Hospital of Ningbo University from January 2020 to May 2021 and were pathologically diagnosed as invasive ductal carcinoma were included in invasive ductal carcinoma group,and 45 patients(49 lesions)with benign breast lesions were included in benign lesion group during the same period.The difference of peritumoral edema between two groups and the relationship between different pathological features of invasive ductal carcinoma and peritumoral edema were compared.Results The peritumoral edema in benign lesion group was significantly less severe than that in invasive ductal carcinoma group(χ2=25.330,P<0.05).The tumor size of invasive ductal carcinoma group was positively correlated with the degree of peritumoral edema(r=0.381,P<0.05).There were significant differences in molecular type,histological grade,T stage,lymph node metastasis and Ki-67 expression level among patients with different peritumoral edema grades(P<0.05).Ki-67 expression level and the number of lymph node metastasis were positively correlated with the degree of peritumoral edema(r=0.348,0.273,P<0.05).Conclusion The degree of peritumoral edema in MRI correlates with the aggressiveness of breast invasive ductal carcinoma and can be used as one of the tools to evaluate breast carcinoma.