Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL) is a T cell subtype of non-Hodgkin's lymphoma (NHL). Typically, lymphoma rarely infiltrates vascular structure. In this article, we present a case of retroperitoneal ALK-positive ALCL with splenic venous tumor thrombosis. A 62-year-old patient presented to our institute with the symptoms of epigastric pain, abdominal distension, and reduced bowel movement. Physical examination indicated no enlarged peripheral lymph nodes or abdominal mass. Laboratory workup revealed granulocytosis, abnormal coagulation function, and normal level of lactic dehydrogenase (LDH). Contrast-enhanced computed tomography (CT) showed a retroperitoneal mass with involvement of pancreas and duodenum and formation of splenic venous tumor thrombus. Ultrasonography-guided retroperitoneal lesion biopsy confirmed the diagnosis of ALK-positive ALCL. The patient was able to tolerate oral intake after two cycles of chemotherapy and showed no sign of lymphoma by positron emission tomography (PET)-CT after the fourth cycle of chemotherapy. In spite of its rarity, lymphoma should be taken into account as a differential diagnosis of other malignancies with tumor thrombosis.