Abstract An 11‐year‐old female cinnamon cockatiel (Nymphicus hollandicus) was presented with a coelomic distention. Dystocia was suspected, given its previous history of a calcium‐deficient diet and multiple instances of nonobstructive dystocia. Exploratory coeliotomy revealed a large intraluminal mass extending through the magnum to the uterus (shell gland). Metastasis and multiorgan involvement were not seen. Histopathologically, malignant and invasive fascicles of spindle cells were associated with abundant myxoid matrix and hypocellular areas. Multinucleation, bizarre cells and atypical mitotic figures were prominent. Masson's trichrome staining verified the muscular origin, and the myxoid matrix was demonstrated utilizing Alcian blue. The neoplastic cells exhibited alpha‐smooth muscle actin and desmin immunoreactivity and were negative for vimentin. Thus, the patient was diagnosed with oviductal and uterine myxoid leiomyosarcoma (LMS). The patient survived 34 days post‐surgery before death associated with suspected enteritis. Myxoid LMS is an extremely rare neoplasm in animals. To our knowledge, myxoid LMS has not been reported previously in pet birds.