Multidrug resistance (MDR) is a main cause of failure in the chemotherapeutic treatment of malignant disorders. One of the well-known genes responsible for drug resistance is multidrug resistance-associated protein (MRP1) gene. The association of MRP1 with clinical drug resistance has not systematically been investigated in Iranian pediatric leukemia patients. We aimed to use real-time RT-PCR technology to study the association between the MRP1 gene and MDR phenotype in Iranian pediatric leukemia patients. We found that overexpression of MRP1 occurred in most of the Iranian pediatric leukemia patients at relapse. No relation between MRP1 mRNA level and other clinical characteristics including cytogenetic subgroups and FAB subtypes was found.