Rhipicephalus (Boophilus) microplus ticks represent a strong problem in cattle production systems in the Mexican humid tropics. For the control, various chemical products are applied with negative implications such as high costs, bioresistance, environmental impact and residues in milk and meat. The objective of this research was to evaluate the in vitro pathogenicity of Metarhizium anisopliae strains MM0801 and CD0804 on Rhipicephalus (Boophilus) microplus ticks. Five concentrations 3x104, 3x105, 3x106, 3x107, 2.6x108 of conidia per ml of M. anisopliae were evaluated on ticks in adult stage collected live from cattle from the dairy basin of Catazajá, Chiapas, Mexico. Ticks were susceptible to the entomopathogenic fungus, finding a mortality of 50% where the mean lethal concentration obtained was 6.58x106 conidia per ml of strain MM0801. It is concluded that M. anisopliae has high pathogenicity on the tick, which may be an alternative for the biological control of the tick in the humid Mexican tropics.