A rare case of uterine leiomyosarcoma associated with chondriod metaplasia, cystic endometrial polyps and uterine horn intussusception in a greater cane rat was macroscopically, histopathologically, immuno-histochemically and ultrastructurally evaluated. The histopathological findings for this tumour were similar to those for leiomyosarcomas described in other species. Immunohistochemical examination demonstrated positive immunoreactivity of neoplastic cells with α-smooth muscle actin, desmin and vimentin. Ultrastructurally, nuclear and cytoplasmic features were consistent with leiomyosarcoma. These results revealed the tumour to be of smooth muscle origin. To our knowledge, this is the first reported case of uterine leiomyosarcoma associated with cystic endometrial polyps, chondriod metaplasia and uterine horn intussusception in a greater cane rat.