Objective To investigate the changes of Treg cells,Th17 cells and related cytokines in pe?ripheral blood of patients with severe hand?foot?mouth disease( HFMD) in the initial stage of infection caused by Enterovirus 71 virus. Methods Thirty?five cases of severe HFMD children in the Fifth Hospital of Shijiazhuang from May 2013 to December 2013 were selected as the research subjects,including 27 cases of severe formed group and 8 cases of danger severe formed group. The frequencies of Th17 cells ( CD3+CD8?IL?17+) and Treg cells( CD4+CD25+Foxp3+) in peripheral blood were detected by flow cytometry in patients with severe HFMD and 31 healthy children(control group). Moreover the serum levels of interleukin 6(IL?6),interleukin 17(IL?17) ,interleukin 10( IL?10) ,interleukin 23( IL?23) ,and human transforming growth factorβ1 ( TGF?β1) were measured by ELISA. Results As compared with those in control group,the frequencies of Treg cells,ratio of Treg/Th17,serum levels of TGF?β1, IL?10 in severe HFMD groups were significantly decreased ( F=23. 23, 30. 88,10. 766,11. 680 respectively;P<0. 05) . However the frequency of Th17 cells,serum levels of IL?6,IL?17,IL?23 in severe HFMD groups were significantly increased( F=646. 81,5. 904,10. 557,3. 490 respectively;P<0. 05) . Conclusion The changes of Treg and Thl7 cells and related cytokines appear in peripheral blood of patients with HFMD in the initial stage of infection caused by Enterovirus 71 virus. The frequency of Treg cell is decreased,however,the frequency of Thl7 cells frequency is increased,as a result,which may spread inflammato?ry reaction and cause complication.