We screened natural products to find compounds with anti-osteoporotic potential using a coculture-based system by which osteoclast differentiation is effectively achieved. We found that methylene chloride soluble fraction of the root of Salvia miltiorrhiza Bunge (Labiatae) suppressed osteoclast differentiation. Five tanshinones, tanshinone IIA (1), tanshinone 1 (2), cryptotanshinone (3), 15,16-dihydrotanshinone I (4), and ferruginol (5) were subsequently isolated from fraction. Among the five compounds, compounds 1-4 reduced the formation of TRAP-positive multinuclear osteoclasts. These results suggest that the identified tanshinones may be useful candidates for development of therapeutic agents to treat osteoporosis and other bone-resorptive diseases.