Objective:To study the expression of CXCL 8 in the serum and CXCL8 mRNA in the peripheral blood mononuclear cells(PBMCs) of the children with Mycoplasma pneumoniae pneumonia (MPP) and its clinical significance.Methods: Forty-eight children(severe cases 12,light cases 36) with MPP were recruited from October 2013 to March 2015 in the Maternal and Child Health-Care Hospital of Huainan.The concentration of the CXCL8 in serum and the level of CXCL8 mRNA in the PBMCs were measured by enzyme linked immunosorbent assay ( ELISA) and polymerase chain reaction ( PCR).Taking GAPDH as the internal reference ,the ratio of lgcDNA/lgGAPDH was regarded as the extreme level of CXCL 8 mRNA.Results: The serum level of CXCL8 and expression of CXCL8 mRNA in PBMCs in the children with MPP were ( 298.917 ±51.860 ) pg/ml and ( 1.848 ±0.525 ) lgcDNA/lgGAPDH.Compared with the normal control ,there were significant differences between the two groups ( P<0.05 ) .Further observation showed that the levels of CXCL8 in serum were no significant difference between in light cases and severe illness (P>0.05).However, the expression of CXCL8 mRNA in peripheral blood of the children with severe illness was significantly higher than those in light cases (P<0.05).Intravenous infusion of Erythromycin was provided in the acute phase for seven to ten days ,so that the children′s condition could be significantly controlled , and the symptoms of pulmonary inflammation were also relieved .Followed by the use of sequential therapy of Azithromycin for about two to three weeks ,the children′s condition were gradually from acute stage to recovery stage .At this time,the CXCL8 and its mRNA levels in peripheral blood of the sick children were all significantly decreased comparing with those in the acute stage(P<0.05).Conclusion: The expression of CXCL8 and its mRNA were increased in the peripheral blood of the sick children with Mycoplasma pneumonia ,and also correlated with the severity of the disease .CXCL8 can participate in the pathogenesis of Mycoplasma pneumonia ,and has a certain cue effect on the severity and prognosis of the disease .Azithromycin can reduce the content of CXCL8 in serum of the sick children via the pathway of inhibiting the proliferation of Mycoplasma pneumoniae ,and down regulate the expression of mRNA ,so that the immune injury mediated by Mycoplasma pneumoniae may be gradually inhibited .