Abstract: Objective To evaluate the clinical significance of minimal residual disease (MRD)detecion in ALL-B of children by flow cytometric (FCM).Methods 52 cases of children with ALL-B were performed bone marrow MRD by FCM analisis after induction therapy,3 moths therapy,and 6 moths therapy.After that,MRD detection was performed every 6 months. According to disease risks, three group were categorized,standard risk (SR),imidiete risk (IR) and high risk(HR).Results After 6 months,SR groups MRD positive cases were 4/21(19 %),IR groups MRD position cases were 8/23 (35 %),HR groups MRD position cases were 5/8 (63 %).9 cases relapsed in all 52 patients.There were significant differrence in replased rate between the positive and negtive MRD (P<0.001). Conclution The dynamic detection of MRD by FCM can be used to evaluate the therapeutic effect and prognosis of children with ALL-B. It is also useful in adjusting treatment strategy and for following up in children with ALL.