【Abstract】 Objective To investigate the effect of fluoride on the expression of UCHL1 during SD rat tooth germ development. Methods 9 pregnant SD rats were randomly divided into 3 groups. Rats in each group were fed with water containing fluoride of 0mg/L, 50mg/L and 200mg/L, respectively. The first mandibular molar germs of fetal rats were obtained at E21 days to make sections for detecting UCHL1 by immunohistochemically method，and to extraction of tooth germ tissue for detecting mRNA by realtime PCR. ImagePro Plus 60 software were used to analyze the results of immunohistochemistry. Results The stain of UCHL1 of the two experimental groups was at lower level than control group, especially in the high fluoride concentration group (200 mg/L). The expression of UCHL1 mRNA is also the same. Conclusion Under the action of fluoride, the expression of UCHL1 in ameloblasts of secretory phase decreased, which may be related to the mechanism of dental fluorosis.