Abstract: In this paper,57 cases of recurrent aphthous ulcer treated with 1% syrup of zinc sulfate mouth were reported,the rate of effectiveness was 80.7%. Changes of serum zinc,hair zinc,immune components and alkaline phospholipidase activities before and after treatment were examined. The serum zinc levels before treatment were lower than normal, but after treatment,they increasec obviously,therefore,the changes of serum zinc may be considered as the bases of recurrent aphthous ulcer therapy.