The paper presents a case of leiomyosarcoma of the gastrointestinal tract in a bearded dragon (Pogona vitticeps) with an ultrasound and histopathological description of pathological changes. According to our knowledge, leiomyosarcoma of the gastrointestinal tract and its ultrasound features have not been reported in lizards yet. A male bearded dragon (Pogona vitticeps), aged 4 years, was referred for radiological and ultrasound examination with a history of apathy and loss of appetite. A preliminary diagnosis of an advanced neoplasia process in the caudal coelomic cavity was established by diagnostic imaging methods. The owner decided to euthanize the animal and agreed to a post-mortem examination. After euthanasia, a histopathological examination was performed. In a radiological examination, an irregularly marginated radiopacity measuring 5.8 x 4.0 cm was visible in the central part of the coelom. Serosal margin details in the coelomic cavity were decreased, and differentiation of coelomic organs was impossible. An ultrasound examination confirmed a large amount of free echogenic fluid in the coelomic cavity. The liver had increased echogenicity, and a hypoechoic focal lesion was found in the right lobe. Mixed echogenicity masses were visible in the caudal coelom adjacent to the small intestinal loops. In one of the adjacent intestinal loops, a focal thickening of the small intestinal wall was observed with loss of the normal layered architecture. The mass had complex and mostly low echogenicity with a cystic lesion present in the centre. Necropsy confirmed the presence of proliferative lesions in the body cavity, originating from the intestine and infiltrating the mesentery and the lumbar spine area as well as the gonads located at this site. On the basis of the histological structure of the intestinal tumour, the neoplastic proliferation was classified, according to the WHO classification, to a group of malignant tumours with characteristics of leiomyosarcoma and arising from the smooth muscles. The ultrasonographic features of gastrointestinal leiomyosarcoma in that lizard corresponded to features found in dogs, in which such tumours occur as eccentric, poorly echogenic masses with anechoic cavities in large changes. Leiomyosarcoma in reptiles can be locally invasive as well. Metastatic foci are also possible, especially in the liver.