Basic hematological information about the avian in its natural habitat is limited. In this study we aimed at investigating, in the peripherical blood of the roadside hawk, Buteo magnirostris, the number of thrombocytes and their morphological, cytochemical and ultrastructural aspects. Blood smears were submited to the following methods: Leishman for morphological analysis and specific methods for the characterization of four kinds of macromolecules of different chemical nature: Glycogen, lysosomal enzymes (myeloperoxidase and the acid phosphatase), basic polyaminoacid rich proteins and phospholipids. The average number of thrombocytes was 26.8 x 10³ ± 10,2 / µL. Structurally the thrombocytes present predominantly elliptic shape, with dense and clumped nuclear chromatin. The cytoplasm is clear, vacuolated and may contain one or two purple azurophilic granules at the poles. The thrombocytes presented positive cytochemical reaction to glycogen, polyaminoacid and for acid phosphatase. Ultrastructurally, the thrombocytes appear as elliptical or spherical cells containing Golgi, much smooth endoplasmic reticulum, small mitochondria, dense osmiophilic granules, microtubules at the outermost zone of the cell and large vacuoles connected to the canalicular system or opened to the surface