<p>Fermented plant extracts are known to exhibit antidiabetic effects. However, antidiabetic activity of fermented lettuce extracts (FHE) and dried sweet potatoes with FHE remains unexplored. This study analyzed γ-aminobutyric acid (GABA), antioxidant, and polyphenol levels in such extracts, and an in vivo oral glucose tolerance, an oral sucrose tolerance, and a fasting blood glucose tests were conducted on streptozotocin-induced diabetes mice to determine antidiabetic effects. FHE showed higher GABA, antioxidant, and polyphenol levels than unfermented extract. The blood glucose levels in diabetic mice that were fed FHE and dried sweet potato with FHE were lower than those in mice that were fed distilled water. Mice fed dried sweet potato with FHE extract showed faster recovery and improved insulin sensitivity. These findings suggest that FHE has antidiabetic properties, which can be attributed to its high levels of GABA, antioxidants, and polyphenols, making it a potential candidate for antidiabetic food products. </p>