Anaplasma marginale and piroplasm species are widespread among Brazilian cattle herds. Both of these tick-borne pathogens hamper livestock production and cause a significant economic impact. Although buffaloes have demonstrated a high level of adaptability, data on tick-borne pathogens are scarcely reported in Brazil. Thus, the aim of this study was to screen water buffaloes from the state of Maranhão for piroplasm and A. marginale occurrence using PCR assays. All samples were negative for A. marginale. One of the 287 (0.35%) water buffaloes tested was positive for Theileria sp. Sequencing of the 18S rDNA fragment (356 bp) showed that the Theileria sp. identified was closely related to the T. buffeli /orientalis group. Future studies on the clinical signs of infection and the main vector in this country are needed.