Cantharidin inhibits osteosarcoma growth in vivo and in vitro. The viabilities of 143B (A) and U-2 OS (B) cells after cantharidin treatment at the doses of 0-15 μM for 0-48h were measured by an xCELLigence RTCA DP system. Osteosarcoma growth was suppressed after cantharidin treatment for 28 days in xenograft-bearing nude mice with 143B cells injection into the tibia(n=9): (C) orthotopic tumor growth was dynamically monitored once a week with X-ray using the Image Station In-Vivo FX system, (D) images of the isolated xenograft tumors, (E) tumor volumes, and (F) body weights of mice. Mice in control group were intervened with DMSO in PBS (1/10,000 V/V). DOX (1 mg/kg·body weight) served as positive control. *p < 0.05, **p < 0.01. DOX, doxorubicin.