Biological control based on entomopathogenic fungi is a promising option for controlling ticks on livestock. The objective of this study was to evaluate acaricidal effect of M. anisopliae (Metschnikoff) Sorokin (Ma14 strain) against R. microplus (Canestrini, 1887) on cattle. Thirty heifers naturally infested with R. microplus were divided into three groups of 10 each. One group was sprayed with Ma14 strain at a concentration of 10⁸ conidia/ml and 0.1% Tween 80, the second was sprayed with M. anisopliae Ma34 strain at the same concentration and considered a positive check. The third group remained a nontreated check. Efficacy of Ma14 was 38.3 to 51.3% from the fourth application to the end of the experiment. The Ma14 strain had considerable efficacy against naturally infesting ticks, which makes it a candidate for use in integrated tick management.