ABSTRACT: Objective   To study the effect of fluorine on the ameloblastin gene expression of mouse mus musculus. Methods   On the basis of setting up a model for medium- and high-level dental fluorosis of mus musculus, this research analyzed the space-time expression of ameloblastin in inferior incisor growth period of mus musculus by using in situ hybridization. Results   The results indicated that in control group (drank deionized water), the formation of mus musculus’ inferior incisor was natural, and the tooth surface was semitransparent, ivory white, smooth and glossy. Ameloblastin mRNA was negative under microscope in the ameloblast proliferation differentiation period; it showed weakly positive expression in intra-cellular and new-birth enamel matrix in secretion initial stage. It showed strongly positive expression in intra-cellular and new-birth enamel matrix when it came to secretion phase. There was no positive expression of ameloblastin mRNA in the mature stage. In low-fluorine group (the concentration of F in drinking water was 50mg/L), there were broad or narrow chalkiness, ill enamel-mineral stripes and comparatively good emanel-mineral stripes alternately on the inferior incisor of mus musculus. Ameloblastin mRNA showed weakly positive expression when it developed from dentoenamel junction to new-birth enamel matrix. In high-fluorine group (the concentration of F in drinking water was 150mg/L), there were wide areas of chalkiness and focal enamel damnification on the inferior incisor of mus musculus. Ameloblasts were disorganized under microscope. The exudation of enamel matrix almost stopped in ameloblast secretion phase. Ameloblastin mRNA showed positive expression on the surface of dentoenamel junction of new-birth enamel matrix and dentoenamel junction while the expression discontinued for several times during the exudation of enamel matrix and it showed comparatively strong positive expression in mineralized enamel matrix. Conclusion   Overdosed fluorine can affect the expression of ameloblastin mRNA in ameloblast and enamel matrix, and it can intermittently influence the exudation of enamel matrix at the same time. Then, it will induce ill mineralization of enamel, unsymmetrical mineralization and focal damnification.