Anti-babesial activity was confirmed in an extract of the bark of Curcuma zedoaria. The active ingredients were isolated, and their chemical structures were determined to be zedoalactones A, B, and C based on spectral data. Zedoalactone C is a hitherto unreported compound. The IC50 vales of these active compounds against Babesia gibsoni were compared with a standard drug, diminazene aceturate. The IC50 value of diminazene aceturate was 0.6 microg/mL, while those of zedoalactones A, B, and C were 16.5, 1.6 and 4.2 microg/mL, respectively.