Excessive osteoclast activity underlies bone-destructive diseases including osteoporosis and rheumatoid arthritis. RANKL-induced NF-κB signaling represents a critical pathway driving osteoclastogenesis. Here, we report that methyl carnosate, a naturally occurring diterpene from rosemary, inhibits RANKL-induced osteoclastogenesis with an IC50 of 1.2 μM (95% CI: 0.9521–1.372 μM) and displays greater potency than its parent compound, carnosic acid. Promoter–reporter analysis further indicates atten