This study was aimed to investigate the expression of plasma miR-223 in pediatric acute lymphoblastic leukemia (ALL) in different treatment time point. A total of 64 pediatric ALL samples were selected from patients treated in Beijing Children's Hospital from May 2005 to January 2012, including 30 samples at new diagnosis (ND), 30 samples at complete remission (CR) and 4 samples at relapse. Without RNA extraction, the miR-223 levels in plasma were directly detected by a reverse-transcription quantitative real-time PCR assay. The results indicated that the expression of plasma miR-223 in pediatric ALL was lower at ND but elevated after CR. The miR-223 expression in plasma of relapse patients didn't show significant difference probably due to a few cases of relapse. The miR-223 levels in plasma had not displayed significant difference between TEL-AML1 positive patients and no fusion gene B lineage ALL patients either at ND or at CR. It is concluded that the plasma miR-223 decreases at ND and increases in CR of children with ALL. miR-223 may act as an anti-oncogene and may be taken as a potential predictive biomarker for evaluating the therapeutic effect of leukemia.