Objective: To study the relationship between 26 study factors (relating to immunity, trace elements and ingredients in saliva) in recurrent apthous ulcer (RAU) patients. Methods: The 26 study factors from 60 RAU patients were determined and were analyzed by non-conditional logistic regression. The risk ratio of the 26 study factors was calculated. Results: EsRFc, T8, Serum IgG and Cu were important risk factors, and B lymphocyte, Zn, Salivary C3 and lysozyme from saliva and serum were important protective factors among the many complicated characteristics of RAU. Conclusion: The results of this study have enriched and deepened our recognition of the causes and mechanisms of RAU. We have provided evidence as to the prevention and treatment of the disease.