Objective To identify risk factors for seroma formation and to explore the related prevention and treatment methods.Methods We collected clinical and pathological data of 92 breast cancer patients undergoing modified radical mastectomy in Hu'nan Provincial People's Hospital,from January to September 2016.Seroma formation was studied in relation to age,tumor size,nodal involvement,the number of lymph nodes removed,flap fixation and external compression dressing.Count date were evaluated by the frequency and percentage,comparison between the groups was analyzed by the chi-square test.Multivariate analysis was performed using Logistic regression analysis.Results Seroma occurred in 45.7％ of patients.Age,tumor size,nodal involvement,the number of lymph nodes removed,flap fixation were risk factors of modified radical mastectomy postoperative seroma.In multivariate logistic regression analysis an association of postoperative seroma formation was noted with the number of lymph nodes removed(OR =1.123,95％ CI:1.036-1.218,P ＜ 0.01),age(OR =1.060,95％ CI:1.006-1.116,P＜0.05),flap fixation(OR=0.363,95％CI:0.135-0.977,P ＜0.05).Conclusion The findings suggest that older patients,with extensive lymph node dissection may more likely to form postoperative seroma,flap fixation can reduce the incidence of seroma.