Recurrent aphthous stomatitis is common oral disease in the world. It is characterized by multiple, recurrent, painful ulcer with circumscribed margins, erythematous haloes and yellow or grey floors. Patients with recurrent aphthous stomatitis suffer from its painful ulcer. But unfortunately, its etiology and pathogenesis is not clear and still unknown. So we review etiology and pathogenesis of recurrent aphthous ulcer and wish to propose direction of the future study.