Abstract: Objective To investigate the changes of plasma IL-12p40 level in infants with Kawasaki disease (KD) and the relationships between plasma IL-12p40 level and coronary artery injury (CAI) and between plasma IL-12p40 level and sensitivity to intravenous immunoglobulin treatment. Methods ELISA-sandwich technique was used to detect the plasma IL-12p40 levels of 62 KD infants before and after IVIG treatment and the plasma IL-12p40 levels of 33 healthy controls. C reactive protein (CRP) and Albumin (Alb) level in plasma of KD infants were also detected. Results The plasma IL-12p40 level in KD infants (pg/ml) (M=689.5,P5=263.5,P95=2261.4) was higher than that in healthy controls (M=632.2,P5=226.7,P95=1829.3),and significant difference existed between the two groups (Z=2.821,PM=716.2,P5=282.4,P95=2464.1) was higher than that in the KD infants without CAIs (M=664.1,P5=246.4,P95=1997.3), and significant difference existed between the two groups (Z=2.565,Pr=0.472,Pr=-0.421,PZ=1.523,P>0.05),but in KD infants who were sensitive to IVIG treatment, the plasma IL-12p40 level significantly decreased after the treatment (Z=2.637,PZ=1.685, P>0.05). Conclusion IL-12 may participate in the immune damage caused by KD, and the changes of IL-12p40 level in KD infants may reflect the severity of illness, and can be used to predict the occurrence of CAI and the effect of IVIG treatment.