Abstract： Objective To investigate the correlation between the high mobility group box 1 (HMGB1)and T helper 17 cell/regulatory T cell (Th17/Treg) in peripheral blood of children with allergic rhinitis (AR) and bronchial asthma (BA).Method A prospective study was used to select 113 children and healthy physical examination subjects in the Department of Outpatient and Emergency,the Seventh Medical Center of Chinese PLA General Hospital from March to December 2023.According to clinical symptoms,they were divided into healthy control group (n=25),allergic rhinitis group (AR group,n=28),bronchial asthma group (BA group,n=31) and both groups (AR+BA group,n=29).The lung function,immunoglobulin E (IgE),interleukin (IL)-17 HMGB1 level and Th17/Treg were compared between the four groups.Statistical methods performed by t-test,analysis of variance,and Pearson correlation analysis.Result The results of the forced expiratory volume in the first second (FEV1) in each group showed that,the healthy control group was higher than that in the AR group,BA group and AR+BA group[(96.4±2.5)%,(90.7±4.9)%,(88.6±4.1)%,(82.1±5.5)%,F=47.193,P<0.001],indicating that lung function may be deteriorated in children with AR and BA.The level of HMGB1 in AR group,BA group and AR+BA group was higher than that in the healthy control group[(30.4±12.4) mg/L,(47.2±17.8) mg/L,(51.4±21.8) mg/L and (4.3±2.1) mg/L,F=48.896,all P<0.001].Th17/Treg in AR group,BA group and AR+BA group was higher than that in the healthy control group (0.68±0.14,0.71±0.14,1.36±0.40,0.30±0.07),F=105.547,all P<0.001).Pearson correlation analysis showed that HMGB1 was positively correlated with Th17 (r=0.521,P<0.001),Th17/Treg (r=0.419,P<0.05),IgE (r=0.502,P<0.05),IL-17 (r=0.472,P<0.05),and was negatively correlated with FEV1 (r=-0.645,P<0.001).Conclusion In the pathogenesis of AR combined with BA in children,the level of HMGB1 and the percentage of Th17 cell increased,while the percentage of Treg cell decreased,and there is an imbalance of Th17/Treg.There is a certain relationship between the level of HMGB1 and percentage of Th17 cells,Th17/Treg,IgE,IL-17 and FEV1,the homeostasis of HMGB1 and Th17/Treg may play a certain regulatory role by affecting the expression of cytokines.