Background The immunologic response to allergens mediated by T lymphocytes is an incipient key element in the pathogenesis of asthma,and Th1/Th2 balance is regarded as the core of asthma pathogenesis.Notch is a single-pass transmembrane receptor protein that regulates differentiation,proliferation and apoptosis in a broad range of cells.It is considered that the Notch signal pathway works in every stage of T cell development and differentiation.Whether the pathway of asthma pathogenesis is related to Notch1 remains unknown.This study is aimed to investigate whether the pathway of asthma pathogenesis is related to Notch1 by examining the effect of knockdown of the Notch1 gene by small interfering RNA on T cell differentiation.Methods An OVA-induced asthma mouse model was established.The expression of Notch1 in the tissue and T cells of the lung from asthmatic mice was detected by RT-PCR and West blotting.The expression of Notch1 and cytokine interleukin(IL)-4 and interferon(IFN)-γ in activated lung T cells was detected by RT-PCR and enzyme-linked immunosorbent assay after blocking Notch1 by small interfering RNA.Results The mRNA and protein expression of Notch1 increased significantly both in the lung tissue and lung T cells of asthmatic mice(both P＜0.05).IL-4 decreased and IFN-γ increased significantly in active lung T cells after Notch1 was blocked by Notch1-specific small interfering RNA(IL-4:(2.51±0.51)pg/ml vs 0.64±0.27)pg/ml protein;IFN-γ:(21.72±4.24)pg/ml vs(39.79±4.09)pg/ml protein,P＜0.05).Conclusion This study demonstrated that the Notch1 signal might play a role in the pathogenesis of asthma by its involvement in Th1/Th2 differentiation.