3'4'7-Trihydroxyflavone is a flavonoid from ladino clover, alfalfa, and Albizzia julibrissin. In the present study, we found that 3'4'7-trihydroxyflavone markedly inhibited the receptor activator of nuclear factor kappa B ligand (RANKL) induced osteoclastic differentiation from mouse bone marrow derived macrophages (BMMs). 3'4'7-trihydroxyflavone also reduced the mRNA expression level of osteoclastic marker genes including calcitonin receptor (CTR), Cathepsin K1 v-ATPase V0 subunit d2 (ATP6v0d2), and dendritic cell-specific transmembrane protein (DC-STAMP). In addition, 3'4'7-trihydroxyflavone decreased the bone resorption activity of osteoclasts on dentin slices. We found that 3'4'7-trihydroxyflavone inhibited RANKL-induced expression of nuclear factor of activated T cells c1 (NFATc1), a key transcription factor of osteoclast differentiation. Furthermore, 3'4'7-trihydroxyflavone attenuated RANKL-induced activation of p38 mitogen-activated protein kinase (MAPK) and expression of B lymphocyte-induced maturation protein 1 (Blimp1), a repressor of negative regulators of NFATc1. Taken together, our data suggest that 3'4'7-trihydroxyflavone inhibits osteoclastogenesis via NFATc1.