Although Stemona plants have long been traditionally used as an insecticide and for killing ticks and head lice, there are limited reports on their acaricidal activity. Jansawan et al. (1993) reported the activity of S. collinsiae root extract against R. (B.) microplus.In the present work, 8 identified and 1 unidentified species Stemona grown in Thailand were tested in vitro and in vivo against R. microplus cattle ticks. Our data provide useful information on acaricidal activity against R. microplus of various Stemona plants for further agricultural and pharmaceutical development.