Abstract: Spontaneous neoplastic lesions are often observed in aged experimental ani-mals. The case reported here was a spindle cell sarcoma in mouse. The original site was uterus with distant lymph nodes metaslases. The neoplasma was composed of interlac-ing bundles of elongated spindle cells with palisading of nuclei. Some areas show degen-eration and necrosis. It was not very typical in ordinary appearance of leiomyosarcoma, but a special type of smooth muscle tumours.