Objective To investigate the changes of serum immunoglobulins and complement in children with mycoplasma pneumoniae pneumonia (MPP). Methods 52 children with MPP, 55 children with non-MPP and 33 healthy children were enrolled. The levels of serum immunoglobulins (IgG, IgA and IgM) and complements (C3, C4) were detected. Results Compared with the non-MPP group and healthy control, the levels of IgM, C3 and C4 in MPP group during their acute phase were significantly higher (P<0.05). And among the MPP group the levels of IgM were hisher and C4 were lower than that in the acute phase. Conclusion Immune function disturbance exists in children with MPP. From acute to recovery stage, the level of IgM increased while C4 increased firstly and then decreased. Immune injury may be involved in the pathophysiology of childhood MPP.