Objective To explore the mechanism of Shema Zhichuan Liquid (SZL) for asthma. Methods Forty rats were allocated to normal control group (Group A), model group (Group B),western medicine group (Group C) and SZL group (Group D). Radioimmunoassay was used to observe the levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) and the ratio of cAMP/cGMP.Results After treatment, cAMP level and cAMP/cGMP ratio were increased and cGMP level decereased in Group C and Group D as compared with Group B (P