Objective: Acute lymphoblastic leukemia (ALL) is the most prevalent type of cancer in children. Minimal residual disease (MRD) is still the most important indicator of clinical results and relapse after chemotherapy. Multidrug resistance is the main obstacle to successful treatment. Multidrug resistance-related protein 1 (MRP1) may play a key role in throwing the chemical drug out of cells leading to therapy resistance. This study aims to detect MRP1 protein in the bone marrow cells of children with B-ALL and determine its value as a prognostic factor in comparison with other factors such as DNA index and MRD obtained by flow cytometric measurement. Methods: Bone marrow samples were obtained from children who are diagnosed as B-ALL (n=20) at day 0 (diagnosis) and 15 of therapy. Risk groups’ classification is based on discrimination of age and white cell count on day 0. The expressions of MRP1 levels and DNA index at diagnosis and MRD on the 15th day of treatment in the bone marrow were detected by using flow cytometry. The B-ALL blast cells were stained using anti-CD10, -CD19, -CD20, -CD34, -CD45 monoclonal antibodies. MRP1 content of cells was detected in an intracellular manner. Results: There was no statistically significant difference in MRP1 expression between risk groups and the other prognostic factor as Flow MRD and DNA index. Conclusion: The utilization of MRP1 as a predictive factor may not provide information on the B-ALL prognosis. Our results can help to better understand the nature of MRP1 in B-ALL patients.