The aim of this study was to explore the effect of pachyman, a mushroom extract, on CD4+CD25+ regulatory T cells (Tregs), serum interleukin 4 (IL-4) and interferon γ (IFN-γ) levels in a mouse model of Kawasaki disease. Lactobacillus casei cell wall extract was diluted to 1 mg/ml in PBS and administered to mice by intraperitoneal injection to establish a model of Kawasaki disease. Sixty female mice were used in this study, 40 of which were randomly assigned to a model (normal saline by gavage, n=20) or experimental group (200 mg/kg/day pachyman by gavage, n=20). The remaining 20 mice were disease and treatment-free, and were used as the control group. Compared to the control mice, mice in the model group exhibited a significantly lower percentage of CD4+CD25+ Tregs and significantly higher serum IL-4 and IFN-γ levels (P<0.05). However, CD4+CD25+ Tregs significantly increased and IL-4 and IFN-γ levels significantly decreased in experimental mice following pachyman treatment (P<0.05). Further analysis showed a negative correlation between CD4+CD25+ Tregs and IL-4/IFN-γ levels (P<0.05). In conclusion, pachyman improves immune function in a mouse model of Kawasaki disease by upregulating CD4+CD25+ Tregs, which may inhibit the cytokine secretion of Th1 and Th2 cells.