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The aqueous and chloroform extracts obtained from leaves of Adhatoda vasica were evaluated for acaricidal activity against engorged females of Rhipicephalus microplus and their larvae. No significant mortality of adult ticks was observed in the tested concentration of aqueous extract except at 80%. Whereas, chloroform extract showed a dosedependent increase in adult mortality, and LC50 and LC90 values were determined as 10.47% and 11.74%, respectively. A significant difference in egg hatching of laid eggs was observed at all concentrations tested and 98.55% inhibition of hatching was observed at 12.5% concentration. Dose-dependent larval mortality was observed in larval immersion test with various concentrations of chloroform extract with LC 50 and LC 90 values of 0.51%, and 1.09%, respectively. The results indicate that the chloroform extract of Adhatoda vasica could have very good in vitro acaricidal activities on adult and larval stages of Rhipicephalus microplus ticks. [ABSTRACT FROM AUTHOR]