Abstract: OBJECTIVE To explore the clinical characteristics of the hand,foot,and mouth disease children complicated with bacterial infections and observe the change of immune function so as to provide guidance for clinical treatment and put forward the effective prevention measures.METHODS A total of 104 children with hand,foot,and mouth disease who were hospitalized from Jan 2013 to Oct 2015 were recruited as the study objects and divided into the complicated bacterial infection group with 28 cases and the single viral infection group with 76 cases according to the type of infection.The clinical symptoms,laboratory data（WBC,CRP,PCT,Glu,CK-MB,and ALT）,humoral immunity levels（IgG,IgA,IgM）,cellular immunity levels(CD₃⁺,CD₄⁺,CD₈⁺,CD₁₉⁺),and outcomes were observed and compared between the two groups of children.RESULTS There was significant difference in the number of severe cases,duration of fever,or incidence rate of frequent hyperarousal,vomiting,or hypersomnia between the single viral infection group and the complicated bacterial infection group（P＜0.05）;there was no significant difference in the incidence rate of fever peak,rash,cramp,pulmonary hemorrhage,detection rate of EV71,or mortality rate;the levels of PCT,Glu,CK-MB,and ALT were higher in the complicated bacterial infection group than in the single viral infection group（P＜0.05）;however,there was no significant difference in the WBC or CRP.The levels of CD₃⁺,CD₄⁺,and CD₈⁺were lower in the complicated bacterial infection group than those in the single viral infection group;the levels of CD₁₉⁺,IgA,and IgM were higher in the complicated bacterial infection group than those in the single viral infection group（P＜0.05）.CONCLUSION The clinical manifestations of the children with hand,foot,and mouth disease aggravated after they are complicated with bacterial infections,which may be related to the further aggravation of disorder of cellular,humoral immunity.The PCT has the advantage in differential identification of the complicated bacterial infections,and the surveillance of PCT may facilitate the early discovery of bacterial infections so as to conduct the active treatment and avoid the deterioration of illness condition.