Objective To investigate the expression of splicing factor SF2/ASF in pediatric acute B-lymphoblastic leukemia(B-ALL) cells and in leukemia cell lines treated with chemotherapeutic agents. Methods The protein levels of SF2/ASF were measured in bone marrow samples during preliminary diagnosis and complete remission(CR) B-ALL children by Western blotting; the protein levels of SF2/ASF, before and after vincristine and cytarabine treatment of B-ALL cell line of NALM-6, were also detected by Western blotting. Results Western blotting showed there was a strong SF2/ASF expression in children with preliminarily diagnosed B-ALL children compared with that in children who had complete remission and in children of the control group composed of idiopathic thrombocytopenic purpura(ITP) cases; high expression of SF2/ASF was detected in NALM-6 cell lines, but the expression reduced after treatment with cytarabine and vincristine. Conclusion Splicing factor SF2/ASF was expressed significantly higher in bone marrow of B-ALL children and leukemia cells, but was down-regulated in CR patients and in B-ALL cells treated with cytarabine and vincristine, indicating that SF2/ASF is a practical marker for monitoring outcome of B-ALL treatment.