Over the past two decades, fluoride effects on osteoclasts have been evaluated; however, its molecular mechanisms remain unclear. In this study, we investigated the effect of fluoride on osteoclast formation, function, and regulation using osteoclasts formed from mice bone marrow macrophages treated with the receptor activator of NF-κB ligand and macrophage colony-stimulating factor. Our data showed that fluoride levels ≤ 8 mg/L had no effect on osteoclast formation; however, it significantly reduced osteoclast resorption at 0.5 mg/L. Fluoride activity on bone resorption occurred through the inhibition of nuclear factor of active T cells (NFAT) c1 expression. Furthermore, the expression of its downstream genes, including the dendritic cell-specific transmembrane protein, c-Src, the d2 isoform of vacuolar (H+) ATPase v0 domain, matrix metalloproteinase 9, and cathepsin K were decreased, leading to impaired osteoclast acidification, reduced secretion of proteolytic enzymes, and decreased bone resorption. In summary, our results suggested that fluoride has different roles in osteoclast formation and function. Fluoride ≤ 8 mg/L did not impact osteoclast formation; however, it significantly decreased the resorption activity of newly formed osteoclasts. The molecular mechanism of fluoride action may involve inhibition of NFATc1 and its downstream genes. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 588–595, 2014.