Dogs can act as intermediary hosts, reservoirs, and sentinel animals for zoonotic diseases such as brucellosis, toxoplasmosis and leptospirosis, and human contact with domestic animals can spread these infections. These diseases are globally distributed, and are a uniquely severe health issue, since they can infect a great range of animals, including humans. The purpose of this work was to determine the prevalence of anti-Leptospira spp., anti-Brucella spp., and anti-Toxoplasma gondii antibodies in stray dogs. Blood samples were collected from 181 stray dogs and used for serological diagnosis. Of the analyzed samples, 36.46%, 16.57%, and 9.39% were positive for T. gondii, Leptospira spp., and B. canis. The results indicate that these zoonotic diseases are highly prevalent in stray dogs in the northwestern region of the state of Paraná. The high infection rates for these zoonotics in the canine population is an indication that the environment is contaminated with a variety of different microorganisms, exposing both humans and dogs to different sources of infection. Key words: Brucella canis. Dogs. Leptospira spp. Toxoplasma gondii. Public health. ResumoO contato do homem com alguns animais domésticos faz com que algumas zoonoses como brucelose, toxoplasmose e leptospirose, tornem-se infecções importantes e, com isso os cães atuam como hospedeiros intermediários, reservatórios e animais sentinelas para estas infecções. Essas enfermidades tem distribuição mundial, e é um grave problema de saúde pública, podendo infectar uma grande variedade de animais, entres os quais, se destacam o cão e o homem. O objetivo deste trabalho foi detectar a ocorrência de anticorpos contra Leptospira spp., Brucella spp. eToxoplasma gondii em cães