Aiming the extract of Cordyceps sinensis significantly inhibits airway inflammation, airway hyperresponsiveness, and the infiltration of eosinophils in the airway of rats and may be related to the modulation of T helper (Th)1 and Th2 cells functions. The mechanisms of C. sinensis involved in modulation of suppression inflammation are not yet determined. In this study, the mechanism involved in the extract of C. sinensis–C.S.3-modulated suppression of inflammation was investigated in vivo and in vitro systems. The results showed that C.S.3 reduced airway inflammation in ovalbumin-induced allergic mice. Furthermore, we found C.S.3 could decrease extracellular signal-regulated kinase 1/2 signaling pathway to suppress activity of nuclear factor-κB in lung cells and cultured airway smooth muscle cells. Conclusion C.S.3 may provide clinical applications for asthma in the future.