<p>The objective of the present study was to evaluate the efficacy of <em>Metarhizium anisopliae</em> on the control of <em>Rhipicephalus</em> <em>microplus</em> in cattle infested naturally in the Mexican tropics. The study was carried out on a ranch in the Mexican tropics. Base on the number of adult and immature (larvae and nymphs) <em>R. microplus</em> ticks 20 steers were assigned into two groups of 10 cattle. Animals in the treated group (average of 73.4 y 27.5 adult and immature ticks respectively) were sprayed with a mixture of Ma14+Ma34 of <em>M. anisopliae</em> at a concentration of 1x10<sup>8</sup> conidios/ml. The other group remained as untreated control (average of 77.7 y 24.7 adult and immature ticks respectively) and treated with water+Tween 80. Each group received 4 applications every 14 days. Adult and immature stages of ticks were recorded on days 0, 3, 5, 7 and 14 post-treatment. From the first application treatment to the end of the experiment, animals in the treated group had lower counts (<em>P</em> < 0.05) of adult (30.9-87%) and immature (35.8-72%) ticks. The results demonstrate the efficacy of repeated treatment with the strains Ma14+Ma34 of <em>M. anisopliae</em> can be used as an alternative to control natural infestation of <em>R. microplus</em> on cattle in the Mexican tropics.</p>