Mixed neuroendocrine-non-neuroendocrine neoplasms (MINEN) are rare tumors that consist of at least 30% of both neuroendocrine and non-neuroendocrine components. The data concerning the pathogenesis of MINEN suggest a monoclonal origin. We describe a spontaneously immortalized cell line derived from gastric MINEN called GNEN-1. Primary tumor consisted of components of high-grade neuroendocrine carcinoma and adenocarcinoma. The GNEN-1 cell line was initiated from metastatic tumor cells of peritoneal fluid and expresses a purely neuroendocrine phenotype. The GNEN-1 cell line grows as monolayers and has retained the neuroendocrine phenotype with positivity for chromogranin A in immunohistochemistry. Electron microscopy showed cytoplasmic dense core granules and axon hillocks. The karyotype revealed alterations typical of both adenocarcinoma and neuroendocrine carcinoma such as trisomy 7 and 8. GNEN-1 cells were also positive for stanniocalcin-1, a marker of poor prognosis in gastric carcinomas. Expression of several markers related to neuroendocrine tumors was found. There have been only a few studies on the pathogenesis of MINEN and management of the disease due to the rarity of this tumor type. Here we describe for the first time an immortalized cell line derived from mixed gastric NEN. The GNEN-1 line offers a tool for future research on gastric NEN.