This experiment was performed in order to study the effects of Haepyoyijintang on the pulmonary injury caused by $SO_2$. Healthy adult male rats weighting about 250g were divided into 4 groups- the Normal group, the Control group, the group of Haepyoyijintang administration for 5 days after $SO_2$ gas exposure (Sample I ), and the group of Haepyoyijintang administration for 10 days before and for 5 days after $SO_2$ gas exposure (SampleⅡ). The results were obtained as follows; 1. In the total number of leucocyte, Sample I and Sample II decreased significantly compared with Control group. 2. In the erythrocyte sedimentation rate, Sample I and Sample Ⅱ decreased significantly compared with Control group. 3. In the lung weight, Sample I and Sample II decreased significantly compared with Control group. 4. In the lung TBA level, only Sample II decreased significantly compared with Control group. 5. In the tracheal glycoprotein level, Sample I and Sample II decreased significantly compared with Control group. According to the above results, Haepyoyijintang has significant effects on the pulmonary injury caused by $SO_2$ in rats.