Kaempferol is one of the most common flavonoid that is present in a variety of vegetables and fruits and has effects on bone metabolism. The present study was performed to define the effects of kaempferol on interleukin (IL)-1β-stimulated receptor activator of NF-κB ligand (RANKL)-mediated osteoclast differentiation. Bone marrow cells were harvested from 6-week-old male imprinting control region mice, and the differentiation of osteoclasts from these cells was evaluated by tartrate-resistant acid phosphatase staining and resorption pit formation assay. Phosphorylated extracellular signal-regulated kinase (p-ERK), phosphorylated p38, phosphorylated c-Jun amino-terminal kinase, NF-κB (p65), IκBα, c-Fos, and nuclear factor of activated T cells c1 (NFATc1) expressions were examined by Western blotting and quantitative RT-PCR. Kaempferol inhibits IL-1β-stimulated, RANKL-mediated osteoclast differentiation and also inhibits IL-1β-stimulated, RANKL-mediated phosphorylation of ERK 1/2, p38 and JNK MAP kinases, and expressions of c-Fos and NFATc1. These results indicate that kaempferol has an inhibitory role in the bone loss by preventing osteoclast formation and suggest that it might be a novel therapeutic agent for the treatment of inflammatory arthritis by managing bone destruction.