To investigate the expression of myeloid-related protein complex (MRP-8/14) in children with acute Kawasaki Disease (KD).A total of 41 children with acute KD and 40 age- and sex-matched control children with upper respiratory tract infection were recruited. Serum levels of MRP-8/MRP-14 complex were measured by ELISA, messenger ribonucleic acid (mRNA) abundance of MRP-8 and MRP-14 in circulating granulocytes and monocytes was determined by RT-PCR, and the number of circulating endothelial cells was determined by flow cytometry.When the analysis was stratified according to the presence or absence of coronary artery ectasia in the KD patient group, serum levels of MRP-8/MRP-14 complex, MRP-8 and MRP-14 mRNA abundance in granulocytes, and the number of circulating endothelial cells were all significantly higher in KD patients with coronary artery ectasia than in KD patients without coronary artery ectasia (P<0.05). Serum levels of MRP-8/MRP-14 complex were positively correlated with the number of endothelial cells in the circulation (r=0.69, P<0.05).Serum levels of MRP-8/MRP-14 complex are elevated in a positive association with the number of circulating endothelial cells in KD children with coronary artery ectasia, suggesting a causative role in the development of coronary artery lesions.