OBJECTIVE: To study the expression of nm23-H1 gene in children with acute lymphoblastic leukemia (ALL) and the relationship between nm23-H1 expression and immunophenotype. METHODS: nm23-H1 expression was measured by semiquantitative RT-PCR in children with ALL (newly diagnosed, n=40; remission, n=32; relapse, n=16; refractory, n=3). Twenty normal children served as the control group. The relationship between nm23-H1 expression and immunophenotype was evaluated. RESULTS: The expression of nm23-H1 in the newly diagnosed ALL group was significantly higher than that in the control (P<0.01) and the remission groups (P<0.01). There was no difference in the nm23-H1 expression between the remission and the control groups. The expression of nm23-H1 in the relapse group was significantly higher than that in the control (P<0.01) and the remission groups (P<0.01), and similar to that in the newly diagnosed ALL group. The three children with refractory ALL had higher nm23-H1 expression. Both the positive rate and expression of nm23-H1 in children with T-lineage ALL were higher than in children with B-lineage ALL (P<0.05). CONCLUSIONS: The expression level of nm23-H1 varies with the stages of ALL. Newly diagnosed, relapsed and refractory ALL children have higher nm23-H1 expression. High nm23-H1 expression may be associated with a poor prognosis and relapse. A higher expression of nm23-H1 in children with T-ALL may be contributed to a low remission rate and a poor prognosis.［Chin J Contemp Pediatr, 2009, 11 (11):881-884］