Background: Xiaoqinglong decoction (XQLD) is a classic Chinese medicinal formula that is widely used to treat allergic asthma. Recently, the use of XQLD to treat allergic asthma has inspired research to deter-mine its mechanism of action. Because dendritic cells (DCs) and the T helper 1 (Th1)/Th2 cytokine balance play important roles in allergic asthma, the present work aimed to assess how these immune system components are affected by XQLD. Methods: Thirty-six female BALB/C mice were randomly divided into three groups: an ovalbumin-based allergic asthma model group, a XQLD treatment group, and a control group. Histology was performed with haematoxylin and eosin staining and immunohistochemical staining. Bronchoalveolar lavage fluid and blood were collected from the animals and used to analyze the composition of inflammatory cells and expression levels of the cytokines interleukin (IL)-5 and IL-13. The thymic stromal lymphopoietin (TSLP) protein expression was assessed by west blot analysis, and the Gata3 and Tbx21 mRNA levels were assessed by polymerase chain reaction. Results: Compared with the OVA group, the levels of TSLP expression, IL-5, IL-13, and immunoglobulin E in the XQLD group were lower (all P < .01). The level of IL-4-expressing cells (Th2 cells) was lower (P ＝ .0013), and the percentage of IFN-γ-expressing cells (Th1 cells) was higher in the XQLD group compared with those in the OVA group (P＝.0065). In addition, XQLD increased the expression of Tbx21 mRNA and decreased the expression of Gata3 mRNA in the lungs compared with the OVA group (both P<.01). Conclusion: These findings suggest that XQLD may ameliorate the course of allergic asthma by regulating the Gata3/Tbx21 balance and inhibiting TSLP expression, changes which are indicative of an altered Th1/Th2 balance. Thus, the clinical effectiveness of XQLD in treating allergic asthma may be due to its regulation of Th1/Th2 balance.