Aims Glucagon‐like peptide‐1 (GLP‐1) is an important modulator of insulin secretion by endocrine pancreas. In the present study, we investigated the effect of swim training on GLP‐1 insulinotropic action in pancreatic islets from monosodium glutamate (MSG)‐obese rats. Methods Obesity was induced by neonatal MSG administration. MSG‐obese and control (CON) exercised rats swam for 30 min (3 times week−1) for 10 weeks. Pancreatic islets were isolated by colagenase technique and incubated with low (5.6 mm) or high (16.7 mm) glucose concentrations in the presence or absence of GLP‐1 (10 nm). In addition, GLP‐1 gene expression in ileum was quantified in fasting and glucose conditions. Results Exercise reduced obesity and hyperinsulinemia in MSG‐obese rats. Swim training also inhibited glucose‐induced insulin secretion in islets from both groups. Islets from MSG‐obese rats maintained GLP‐1 insulinotropic response in low glucose concentration. In contrast, in the presence of high glucose concentration, GLP‐1 insulinotropic action was absent in islets from MSG‐obese rats. Islets from MSG‐exercised rats showed reduced GLP‐1 insulinotropic action in the presence of low glucose. However, in high glucose concentration swim training restored GLP‐1 insulinotropic response in islets from MSG‐obese rats. In all groups, glucose intake increased GLP‐1immunoreactivity and gene expression in ileum cells in relation to fasting conditions. Swim training reduced these parameters only in ileum cells from CON‐exercised rats. Neither MSG treatment nor exercise affected GLP‐1 expression in the ileum. Conclusions Exercise avoids insulin hypersecretion restoring GLP‐1's insulinotropic action in pancreatic islets from MSG‐obese rats.