Objective To evaluate the regulatory effect of recombinant human interferon α1b(rhIFN-α1b)on immune function of children with infectious mononucleosis (IM) through regulating the expression of Foxp3. Methods 98 children with IM treated in the department of pediatrics of a hospital from March 2019 to March 2020 were randomly divided into interferon group (n=49) and ganciclovir group (n=49) by simple randomized number table method. Interferon group received rhIFN-α1b atomization inhalation treatment, ganciclovir group received ganciclovir intravenous drip, treatment courses were both 7 days. Clinical efficacy and safety of two groups of children were observed, expression level of Foxp3 mRNA in peripheral blood mononuclear cells (PBMC), immune function and serum-related cytokines of two groups of children before and after treatment were compared. Results The total effective rate and negative conversion rate of serum EB virus DNA (EBV-DNA) in interferon group were both higher than those in ganciclovir group (87.8% [43/49] vs 71.4% [35/49], 89.8% [44/49] vs 73.5% [36/49]; both P < 0.05). Compared with ganciclovir group, children in interferon group had shorter time of heat course and pharyngitis, shorter recovery time of abnormal laboratory indexes (leukocyte count, proportion of hetero-lymphocytes, ala-nine aminotransferase [ALT], creatine kinase isoenzyme MB [CK-MB]), and shorter hospitalization time (all P < 0.05). The Levels of peripheral blood CD3⁺ and CD8⁺, as well as serum tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in both groups of patients after treatment decreased compared with those before treatment (all P < 0.05), the values of CD4⁺ and CD4⁺/CD8⁺ in peripheral blood, expression level of Foxp3 mRNA in PBMC, as well as concentrations of serum immunoglobulin A(IgA), IgG and interleukin-2(IL-2) in both groups were all hi-gher than those before treatment (all P < 0.05); however, the improvement was more obvious in interferon group (all P < 0.05). The adverse reaction rate of interferon group was lower than that of control group (4.1% vs 20.4%, P < 0.05). Conclusion rhIFN- α1b may correct the abnormal cellular immune function of children with IM and improve their humoral immune level by up-regulating the expression level of Foxp3 mRNA in PBMC.