A nymph of Amblyomma triste Koch, 1844 was found on a bat Myotis albescens (E. Geoffroy 1806) (Vespertilionidae), captured in Cerro Pan de Azúcar (34°47´S 55°13´W), Departamento Maldonado, Uruguay. A retrospective search of ticks from bats deposited in the Museo Nacional de Historia Natural, Montevideo, Uruguay, yielded seven larvae of Ornithodoros mimon Kohls, Clifford & Jones, 1969, from Eptesicus furinalis (d´Orbigny 1847) (Vespertilionidae), captured in Departamento Cerro Largo; six larvae were collected at Estancia La Formosa, (31°51´S 54°12´W), north to the locality of Aceguá, and one larva was collected at Arroyo Sarandí (32°29´S 53°41´W). This is the first record of A. triste from Chiroptera, but it is doubtful that bats are important in the life cycle of this tick species. The present records of O. mimon are the first since the description of this species from larvae collected on Bolivian and Uruguayan bats more than 30 years ago.