ABSTRACT. Figueiredo F.B., de Vasconcelos T.C.B., Reis R.S. & Pereira S.A. [Histoplasma capsulatum natural infection in the dog living at southern zone in the Municipality of Rio de Janeiro, RJ - Case report.] Infecção natural por Histoplasma capsulatum em cão residente em bairro da zona sul do município do Rio de Janeiro - Relato de caso. Revista Brasileira de Medicina Veteriná- ria, 38(2):125-127, 2016. Laboratório de Pesquisa Clínica em Dermatozoonoses em Animais Domésticos, Instituto Nacional de Infectologia Evandro Chagas, Fundação Instituto Oswaldo Cruz, Av. Brasil, 4365, Manguinhos, RJ 21040-360, Brasil. E-mail: firstname.lastname@example.org Histoplasmosis is a fungal infection with a wide clinical spectrum, from asymptomatic to lethal disseminated disease. Its etiological agent, Histoplasma capsulatum, is found in excreta of birds and bats. We report a fatal canine histoplasmosis case affectingaa dog resident in an apartment in an urban area of the municipality of Rio de Janeiro. The mycological diagnosis was confirmed by blood culture and this finding highlights the importance of the dog as a sentinel for human exposure to the pathogen. We suggest epidemiological research and inclusion of histoplasmosis in the differential diagnosis of canine disorders that, even non-specific, are associated with environmental conditions favorable to the presence of H. capsulatum. We also alert to the need of stimulus in order to the both veterinary and medical qualification for the benefit of early diagnosis.