Osteolytic bone metastasis frequently occurs in the later stages of breast, lung, and several other cancers. Osteoclasts, the only cells that resorb bone, are hijacked by tumor cells, which break down bone remodeling systems. As a result, osteolysis occurs and may cause patients to suffer bone fractures, pain, and hypercalcemia. It is important to understand the mechanism of bone metastasis to establish new cancer therapies. MicroRNAs are small, noncoding RNAs that are involved in various biological processes, including cellular differentiation, proliferation, apoptosis, and tumorigenesis. MicroRNAs have significant clinical potential, including their use as new therapeutic targets and disease-specific biomarkers. Recent studies have revealed that microRNAs are involved in osteoclast differentiation and osteolytic bone metastasis. In this review focusing on microRNAs, the author discusses the roles of microRNAs in osteoclastogenesis and osteolytic bone metastasis.