Many bone-related diseases such as osteoporosis, rheumatoid arthritis are occurred by excessive bone resorbing activity of osteoclasts. Recently, many studies have been proceeded to find out the new therapeutic materials from natural products of plants. Phlomis umbrosa Turcz, one of the natural products of plants has been known to improve bone health. However, the precise effects and treatment mechanisms of Phlomis umbrosa Turcz about bone diseases has been unknown. So, we examined the effects of Phlomis umbrosa Turcz on expression of receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation in bone marrow-derived macrophages (BMMs) and bone resorption. Also, we investigated the treatment mechanisms of Phlomis umbrosa Turcz relating to osteoclast differentiation. Here, we showed that Phlomis umbrosa Turcz significantly suppressed RANKLinduced osteoclast differentiation and bone resportion. Furthermore, Phlomis umbrosa Turcz suppressed the activation of NF-κB in bone marrow macrophage treated RANKL and M-CSF. The mRNA expression of c-Fos, nuclear factor of activated T-cells (NFAT)c1, osteoclast-associated receptor (OSCAR), tartrate-resistant acid phosphatase (TRAP) in BMMs was inhibited by Phlomis umbrosa Turcz. Integrin αν, β3 relating to cell adhesion and dendritic cell-specific transmembrane protein (DC-STAMP) relating to the structure of filamentous actin (F-actin) ring and cathepsin K relating to bone resorbing activity are disrupted too. These results suggest that Phlomis umbrosa Turcz will be a good materials to treat bone diseases like osteoporosis.