100 cases of recurrent aphthous ulcer (RAU) were randomly divided into two groups, 55 cases in the experimental group who were given traditional Chinese medicine Zhong tong'an capsules combined with dexamethasone tablets, while 45 cases in the control group who were given dexamethasone tablets alone. The course of treatment was 9 days, and follow up period was 6 months. The overall effective rates were 94.45% and 77.78% in the experimental group and the control group respectively. There was significant difference between the two groups in the treatment outcome (P < 0.05).