The incidence of leiomyosarcomas (LMS) has declined drastically. In fact, the introduction of immunohistochemistry (IHC) helped to differentiate LMS from other gastrointestinal stromal tumors (GIST) by receptor tyrosine kinase (KIT)-mutation detection making gastric LMS a sporadic tumor recently. We report a 60-year-old female who presented with a three-week history of abdominal pain. An abdominal computed tomography scan showed a large exophytic mass (22 ×19 ×15 cm) arising from the greater curvature of the stomach with multiple metastases. A biopsy was taken, and the initial histopathological examination was suggestive of GIST. However, further histopathological examination confirmed a high-grade gastric LMS. The patient refused any surgical intervention. Therefore, the patient had only received chemotherapy. On 9-month follow-up, the patient is still alive without disease progression. In conclusion, gastric LMS is a rare tumor. Due to the possibility of being misdiagnosed with other GIST, extensive pathological evaluation through specialized experts and IHC analysis is recommended.