This experiment was performed in order to study the effects of Gyumsuyukgunjun on the injured tracheal tissue induced $SO_2$ in rats. Healthy adult male rats weighting about 250g were divided into 4 groups - the Normal group, the Control group, the group of Gyumsuyukgunjun administration for 5 days after $SO_2$ gas exposure (Sample I), and the group of Gyurnsuyukgunjun administration for 10 days before and for 5 days after $SO_2$ gas exposure (Sample II). The results were obtained as follows ; 1. In the trachea Control group, the lesion of the ciliated epithelium was severe and the mucus secretion of the respiratory tract was increased significantly. 2. In the trachea of Sample I group, the lesion of the ciliated epithelium and the mucus secretion of the respiratory tract were decreased compared with Control group. 3. In the trachea of Sample II group, the lesion of the ciliated epithelium and the mucus secretion of the respiratory tract were decreased compared with Control and Sample I group. According to the above results, Gyumsuyukgnjun has significant effects on the injuried tracheal tissue caused by $SO_2$ in rats.