Abstract: OBJECTIVE To observe and study the changes of peripheral blood lymphocyte subsets and NK cell of children with infectious mononucleosis,in order to provide evidence for the immunoregulation of children with the disease.METHODS A total of 56 children with infectious mononucleosis in hospital from Apr.2014 to Nov.2015 were selected as the observation group,and 56 healthy children at the same period were selected as the control group.The peripheral blood lymphocyte subsets and NK cell of children were detected and analyzed to understanding the changes.The detection results were compared between children with different white blood cell levels and the relationship between these data and infectious mononucleosis were studied by the logistic analysis.RESULTS The peripheral blood CD₁₉⁺,CD₁₆⁺CD₅₆⁺and CD₃⁺CD₄⁺,CD₄⁺and CD-4⁺/CD₈⁺in observation group were all lower than control group,but CH₈⁺higher than control group,and the difference was statistically significant（P＜0.05）;The detection results of observation group with different white blood cell levels had obvious differences（P＜0.05）,and those peripheral blood lymphocyte subsets and NK cell indexes all had close relationship to infectious mononucleosis by the Logistic analysis with statistically significant difference（P＜0.05）.CONCLUSION The change of peripheral blood lymphocyte subsets and NK cell of children with infectious mononucleosis are great,so the immunoregulation of children with infectious mononucleosis should be paid more attention.