OBJECTIVES: The streptozotocin (STZ) model is widely used in diabetes research. However, the cellular and molecular states of pancreatic endocrine cells in this model remain unclear. This study explored the molecular characteristics of islet cells treated with STZ and re-evaluated β-cell dysfunction and regeneration in the STZ model. METHODS: We performed single-cell RNA sequencing of pancreatic endocrine cells from STZ-treated mice. High-quality sequencing data from 2,999 cells were used to identify clusters via Louvain clustering analysis. Principal component analysis (PCA), t-distributed stochastic neighbor embedding (t-SNE), uniform manifold approximation and projection (UMAP), force-directed layout (FDL), and differential expression analysis were used to define the heterogeneity and transcriptomic changes in islet cells. In addition, qPCR and immunofluorescence staining were used to confirm findings from the sequencing data. RESULTS: Untreated β-cells were divided into two populations at the transcriptomic level, a large high-Glut2 expression (Glut2) population and a small low-Glut2 expression (Glut2) population. At the transcriptomic level, Glut2 β-cells in adult mice did not represent a developmentally immature state, although a fraction of genes associated with β-cell maturation and function were downregulated in Glut2 cells. After a single high-dose STZ treatment, most Glut2 cells were killed, but Glut2 cells survived and over time changed to a distinct cell state. We did not observe conversion of Glut2 to Glut2 β-cells up to 9 months after STZ treatment. In addition, we did not detect transcriptomic changes in the non-β endocrine cells or a direct trans-differentiation pathway from the α-cell lineage to the β-cell lineage in the STZ model. CONCLUSIONS: We identified the heterogeneity of β-cells in both physiological and pathological conditions. However, we did not observe conversion of Glut2 to Glut2 β-cells, transcriptomic changes in the non-β endocrine cells, or direct trans-differentiation from the α-cell lineage to the β-cell lineage in the STZ model. Our results clearly define the states of islet cells treated with STZ and allow us to re-evaluate the STZ model widely used in diabetes studies.