Objective To investigate the serum levels of sialic acid, IgG, C3, C4 and SCRPs and analyze the correlations between sialic acids levels and IgG, C3, C4 or SCRPs levels in children with Mycoplasma pneumoniae pneumonia (MPP).Methods A total of 125 children with MPP were included in MPP group and 89 pneumonia children without evidence of M.pneumoniae infection were included in the control group.Sera were collected from the children at both the acute and convalcent stages in the two groups.