Insulin secretion from pancreatic β cells is initiated by membrane potential depolarization, followed by activation of voltage-gated Ca2+ channels to trigger Ca2+-mediated insulin vesicle fusion with the β cell plasma membrane. Here, we show that β cell swelling associated with glucose metabolism was sensed by LRRC8 channel complexes and contributed to insulin secretion. Hypertonic perfusate (360-380 mOsm) dose dependently impaired glucose-stimulated insulin secretion by counteracting β cell swelling. Hypotonic perfusate alone, independent of glucose stimulation or KATP channel closure, was sufficient to increase β cell intracellular Ca2+ and trigger insulin secretion. Inhibition of sodium-potassium-chloride cotransporter-1 with bumetanide, which diminished the intracellular Cl- concentration in β cells and consequently reduced Cl- efflux via LRRC8 channel complexes, also significantly reduced hypotonic-stimulated insulin secretion. Finally, stimulation of insulin secretion by the glucokinase activator GKA50, which is known to induce β cell swelling, was entirely suppressed in β cell-targeted Lrrc8a KO islets. These data support a model wherein the LRRC8 channel complex senses β cell swelling triggered by glucose metabolism and regulates β cell insulin secretion through activation of LRRC8-mediated Cl- efflux.