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Cleistocalyx operculatus flower buds are used as a main ingredient in various beverages and herbal tea in tropical areas. The present study was conducted to investigate anti-osteoclastogenic effects of ethanol extract of C. operculatus flower buds (ECB) and to identify anti-osteoclastogenic compounds in these buds. ECB significantly inhibited RANKL-induced osteoclast differentiation and decreased RANKL-induced the activation of NFATc1. We isolated nineteen compounds from C. operculatus flower buds and found that eight compounds, including maslinic acid (6) and its two coumaroyl analogs (7 and 8), significantly inhibited RANKL-induced osteoclast formation. Among these, 3-O-trans-p-coumaroyl maslinic acid (8) showed the most potent inhibitory effect on RANKL-induced osteoclastogenesis via impairment of c-Fos and NF-κB activation, and subsequently, NFATc1 activation. These results suggested that identification of the anti-osteoclastogenic compounds from C. operculatus flower buds may extend our understanding of molecular mechanisms underlying biological activities of C. operculatus flower buds for osteoclast-related diseases.