Objective : This experiment was performed in order to study the effects of Scrophulariae Radix on the injured tracheal tissue induced So, in rats. Methods : Healthy adult male rats weighting about 250g were divided into 4 groups - the Normal group, the Control group, the group of Scrophulariae Radix administration for 5 days after $SO_2$, gas exposure(Sample I), and the group of Scrophulariae Radix administration for 10 days before and for 5 days after $SO_2$, gas exposure(Sample II). Results : In the trachea Control group, the lesion of the ciliated epithelium was severe and the mucus secretion of the respiratory tract was increased significantly. 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. 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. conclusions : According to the above results, Scrophulariae Radix has significant effects on the injuried tracheal tissue caused by $SO_2$ in rats.