Recurrent fever for five or six days in children may be caused by infectious diseases, connective tissue diseases, tumors and other reasons. 1. Infectious diseases: Bacterial, viral, fungal, mycoplasma, chlamydia and other infections may cause recurrent fever in children. 2. Connective tissue diseases: connective tissue diseases such as systemic lupus erythematosus, ankylosing spondylitis, dermatomyositis, etc. may cause prolonged and recurrent fever, which may result in recurrent fever for five or six days. 3. Tumor: Tumor cells will release endogenous pyrogen to cause fever, while brain tumors or brain metastases can directly infiltrate the thermoregulatory center leading to central fever, such as malignant lymphoma, acute leukemia, renal carcinoma, liver cancer, there may be children with recurrent fever for five or six days. There may be other reasons for children’s recurrent fever for five or six days, so it is recommended to consult the doctor in time, complete the relevant examination, and carry out standardized treatment after clarifying the cause of the disease, so as to avoid delaying the condition.