Abstract The role of Zn²⁺-sensing receptor GPR39 on glucose homeostasis and incretin regulation was assessed in enteroendocrine L- and K-cells. Anti-hyperglycaemic, insulinotropic and incretin secreting properties of Zn²⁺ were explored in normal, diabetic and incretin receptor knockout mice. Compared to intraperitoneal injection, oral administration of Zn²⁺ (50 μmol/kg body weight) with glucose (18 mmol/kg) in lean mice reduced the glycaemic excursion by 25–34% (p < 0.05–p < 0.001) and enhanced glucose-induced insulin release by 46–48% (p < 0.05–p < 0.01). In diabetic mice, orally administered Zn²⁺ lowered glucose by 24–31% (p < 0.01) and augmented insulin release by 32% (p < 0.01). In glucagon like peptide-1 (GLP-1) receptor knockout mice, Zn²⁺ reduced glucose by 15–28% (p < 0.05–p < 0.01) and increased insulin release by 35–43% (p < 0.01). In contrast Zn²⁺ had no effect on responses of glucose-dependent insulinotropic polypeptide (GIP) receptor knockout mice. Consistent with this, Zn²⁺ had no effect on circulating total GLP-1 whereas GIP release was stimulated by 26% (p < 0.05) in lean mice. Immunocytochemistry demonstrated GPR39 expression on mouse enteroendocrine L- and K-cells, GLUTag cells and pGIP/Neo STC-1 cells. Zn²⁺ had a direct effect on GIP secretion from pGIPneo STC-1 cells, increasing GIP secretion by 1.3-fold. GPR39 is expressed on intestinal L- and K-cells, and stimulated GIP secretion plays an integral role in mediating enhanced insulin secretion and glucose tolerance following oral administration of Zn²⁺. This suggests development of potent and selective GPR39 agonists as a therapeutic approach for diabetes.