The acaricidal activity of the 9-oxo-10,11-dehydroageraphorone (euptox A), a cadenine sesquiterpene from Eupatorium adenophorum (E. adenophorum) against Sarcoptes scabiei and Psoroptes cuniculi was tested in vitro. A complementary log–log (CLL) model was used to analyze the data of the toxicity tests in vitro. The results showed euptox A had strong toxicity against mites, killing all S. scabiei at 3 and 4mg/ml (m/v) concentration, while 4mg/ml euptox A was also found to kill all P. cuniculi within a 4h period. Similarly, 2, 3 and 4mg/ml concentration of euptox A had strong toxicity against S. scabiei, with median lethal time (LT 50 ) values at 0.687, 0.526, 0.326h, respectively. 3mg/ml and 4mg/ml showed strong acaricidal action against P. cuniculi; the LT 50 values were 0.693 and 0.493h, respectively. The median lethal concentration (LC 50 ) values were 1.068mg/ml for Scabies mite and 0.902mg/ml for P. cuniculi in 2h. The results indicate that euptox A has strong acaricidal activity and may exploit as novel drugs for the effective control of animal acariasis.