ABSTRACT.- The major surface protein 1a (MSP1a) gene has been used to characterize Anaplasma marginale genetic diversity. This pathogen causes significant productivity and economic losses to the cattle industry. The objective of the present study was to report the first characterization of A. marginale genetic diversity in Uruguay based on MSP1a genotypes and their putative relationship with Rhipicephalus microplus. This cross-sectional study was conducted between 2016 and 2020. The study included whole blood samples from clinical cases of bovine anaplasmosis obtained from 30 outbreaks located in six Uruguay territorial departments. Diagnosis was performed using Giemsa-stained smears and confirmed by nested Polymerase Chance Reaction (nPCR) targeting the A. marginale major surface protein 5 gene. The genetic diversity of A. marginale strains was characterized by analyzing the microsatellite and tandem repeats of MSP1a. Copyright © 2022 Parodi, Armúa-Fernández, Schanzembach, Mir, Benítez-Galeano, Rodríguez-Osorio, Rivero and Venzal.