Abstract: Tumor microenvironment provides a unique environment for tumor development,where the biology behavior of tumor cells is regulated not only by their genetics but also by the surrounding environment.Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) originating from the neuroendocrine cells of the gastroenteropancreatic system are characterized by a propensity to secrete a variety of peptide hormones and biogenic amines.The symptoms of GEP-NENs at early stages are often atypical,thus delaying the diagnosis.A further understanding of the pathobiology of GEP-NENs on the basis of studies on GEP-NENs tumor microenvironment can provide new evidence for clinical diagnosis and treatment.This review aims to introduce different cell types,several proteins involved in extracellular matrix remodeling,some growth factors,and chromogranin A (CgA) in the tumor microenvironment of GEP-NENs,in order to highlight their indispensable roles in GEP-NENs progression.