Objective To investigate the effects of down-regulating of Rfng gene ( 1, 3-Nacetylglucosaminyltransferases) in lung CD4 + T cells of asthmatic rat model by small interfering RNA ( siRNA) and explore the role of Rfng in pathogenesis of asthma. Methods An asthmatic rat model was established by OVA sensitization and challenge. Total T cells were isolated from lung tissue of asthmatic rats, and CD4 + T lymphocytes were purified using magnetic beads. CD4 + T lymphocytes were transfected by siRNA targeting Rfng gene. The mRNA and protein expressions of Rfng were detected by quantitative PCR and Western blot. Quantitative PCR was performed to determine the mRNA levels of Th1 /Th2 cytokines and related genes including IL-12, IFN-γ, IL-4, IL-5, T-bet, and GATA3. ELISA was performed to determine the concentrations of IL-12, IFN-γ, IL-4, and IL-5 in supernatant. Results The mRNA and protein expression of Rfng in RNAi group decreased significantly. IL-12, IFN-γ, T-bet increased and while IL-4, IL-5, and GATA3 decreased significantly. The concentrations of IL-12 and IFN-γ in the supernatant increased significantly, while IL-4 and IL-5 decreased significantly. Conclusions Down regulation of Rfng affects T cell differentiation. It is presumed that Fringe contribute to the pathogenesis of asthma.