Astragaloside IV (AST) is the main active constituent of Radix Astragali, a Chinese herb traditionally used to prevent asthma attack from chronic asthma patients. Its efficacy and action mechanisms in asthma attack prevention remain nonetheless to be further explored. In this study, chronic asthma was induced exposing ovalbumin (OVA) sensitized mice to repeated OVA challenges twice every two weeks for 12 weeks. Mice were treated with AST for 4 weeks just after the final challenge. In this murine model of chronic asthma, the airway dysfunction and remodeling remained severe and was accompanied with suppression of the IFN-gamma level in the bronchoalveolar lavage fluid (BALF) even four weeks after the final challenge, indicating that the airway structural changes continued to develop even after interruption of OVA challenges. However, after AST treatment, the airway hyperresponsiveness was sharply relieved, accompanied by the reduction of collagen deposition and mucus production, meanwhile the inflammatory cells were decreased but the IFN-gamma level increased in BALF. In conclusion, AST could prevent the development of chronic asthma, thus reducing asthma attacks. Our results indicated that it should be used as a supplementary therapy on preventing asthma attacks from chronic asthma patients.