Chagas disease and the leishmaniases are endemic zoonoses of great importance to public health in the state of Piauí, Brazil. The domestic dog (Canis familiaris) is a major reservoir, host of Trypanosoma cruzi and Leishmania spp. in both urban and rural areas, playing an important role in the transmission of these parasites. The present study evaluated the prevalence of both infectious diseases in dogs of a rural area in the municipality of São João do Piauí, Piauí State. One hundred twenty-nine blood samples were collected for serological assessment: for the leishmaniases, 49 (38%) animals tested positive by the Dual-Path Platform technology (DPP), nine (6%) by the Enzyme-linked Immunosorbent Assay (ELISA), and 19 (14.7%) by the Indirect Fluorescent Antibody test (IFA); while for American Trypanosomiasis, 36 (28%) dogs were reagent by ELISA and 21 by IFA. Of the 129 dogs sampled, 76 were submitted to xenodiagnosis, bone marrow aspiration and skin biopsy to perform parasitological tests whose results showed only one (2.3%) positive skin sample for Trypanosoma caninum and one positive xenodiagnosis for T. cruzi, both results confirmed by molecular assays. Three hundred triatomines of the species Triatoma brasiliensis and 552 phlebotomines - 509 (97%) of the species Lutzomyia longipalpis, were also captured.