A 1-year-old, male canary (Serinus canaria) with a history of an enlarged abdomen of several days duration died acutely and was submitted for necropsy. Results revealed a yellow to tan hard mass, 2 cm in diameter, adherent to the cloacal wall. Histologically, the mass was composed of interlacing bundles of pleomorphic spindle cells with numerous and bizarre mitotic figures. Neoplastic cells were positive for vimentin and negative for desmin and actin and showed ultrastructural features (dilated stacks of rough endoplasmic reticulum, intermediate filaments, rare collagen secretion granules, lack of external lamina) typical of fibroblasts. Based on these results, the diagnosis was cloacal fibrosarcoma, previously not reported in canaries.