The current study aimed to investigate the changes and regulatory mechanism of cluster of differentiation (CD)4+CD25high forkhead box protein 3 (Foxp3+) regulatory T cells (Tregs) in childhood B-cell acute lymphocytic leukemia (B-ALL). A total of 18 children with B-ALL and 15 age-matched healthy children were included. Reverse-transcription quantitative polymerase chain reaction was used to evaluate the mRNA levels of Foxp3, cytotoxic T-lymphocyte associated protein 4 (CTLA4), glucocorticoid-induced tumor necrosis factor receptor (GITR), lymphocyte activation gene 3 (LAG3), interleukin (IL)-2 receptor (R)β/γ, IL-6Rα/β, mothers against decapentaplegic homolog (Smad)3/4 and runt-related transcription factor (RUNX)1/3 in CD4-positive cells. The concentration of cytokines in plasma were measured using a cytometric bead array. Additionally, the proportion of CD4+CD25highFoxp3+ Tregs and levels of associated proteins was analyzed using flow cytometry. The results demonstrated that the proportion of CD4+CD25highFoxp3+ and expression of Foxp3 in children with B-ALL was significantly higher compared with healthy controls (P<0.05) and that transcription levels of CTLA4, GITR and LAG3 were also significantly elevated (P<0.05). Compared with healthy controls, the expression of IL-2Rα/β and its downstream molecule phosphorylated signal transducer and activator of transcription 5 (pSTAT5) in CD4-positive cells significantly increased (P<0.05); however, no significant difference of IL-2Rγ levels was identified between the two groups. Correlation analysis demonstrated a significant positive correlation between the expression of phosphorylated (p) signal transducer and activator of transcription factor (STAT)5 and CD4+CD25highFoxp3+ Tregs in children with B-ALL (r=0.17; P<0.05). The plasma concentration of TGF-β, the expression of its receptor TGF-βRI/II and downstream molecules Smad3/4 were significantly upregulated in children with B-ALL (P<0.05), whereas the expression of RUNX1/3 was lower compared with healthy controls (P<0.05). Furthermore, the expression of Smad3 and RUNX1 was positively correlated with CD4+CD25highFoxp3+ Tregs in children with B-ALL (r=0.87 and 0.60, respectively; P<0.05). Additionally, the expression of pSTAT3 in CD4-positive cells decreased significantly in pediatric patients with B-ALL when compared with healthy controls; however, plasma concentrations of IL-6 was significantly higher (P<0.05). Furthermore, a negative correlation was identified between pSTAT3 and CD4+CD25highFoxp3+ Tregs in pediatric patients with B-ALL (r=-0.39; P<0.05). However, no significant differences in IL-6Rα/β expression were identified between the two groups. The results demonstrated that the excessive activation of IL-2/pSTAT5 and TGF-β/Smad signaling, and insufficiency of pSTAT3 may be correlated with increased CD4+CD25highFoxp3+ Tregs in pediatric B-ALL.Keywords: acute B lymphocytic leukemia; interleukin-2; interleukin-6; regulatory T cells; transforming growth factor-β.