Abstract: Objective To evaluate the effects of fluoride varnish on enamel demineralization adjacent to bonded brackets of orthodontic teeth. Methods Patients who needed to extract at least 2 premolars for orthodontic reasons were selected.For each patient,premolars were randomly divided into 2 groups.Brackets were bonded,and only the test teeth were treated with fluoride varnish.After 85 to 95 days,the occurrence of enamel demineralization was investigated; at the same time, surface enamel microhardness were measured by the microhardness test and the enamel lesions because of demineralization were observed with polarized light microscope after the premolars were extracted.The surface morphology of each tooth was observed by scanning electron microscopy. Results The rate of enamel demineralization in the test group was 11.11%; and that in the control group was 44.44 %（P<0.05）; besides,the microhardness of enamel in the test group was significantly greater than that in control group（P<0.05）.The samples in the control group showed obvious demineralization lesions.The mean lesion depths were（40.24±2.76） μm in the test group and（80.35±5.42） μm in the control group,and therer was statistical difference between them（P<0.05）.Many micropores and cellular structures appeared on the enamel surfaces in the control group,however,smooth and intact surfaces were observed on the enamel surfaces treated with fluoride varnish. Conclusions Fluoride varnish can be a kind of effective preventive adjunct in reducing demineralization adjacent to brackets.