In addition to its important role in digestion, absorption and secretion, the gastrointestinal epithelium serves as a barrier to the diffusion of toxins, allergens and pathogens from the luminal contents into the interstitial tissue. Barrier disruption and diffusion of noxious substances are known to induce mucosal inflammation and tissue injury. In fact, the disruption of gut barrier function plays a crucial role in the pathogenesis of numerous gastrointestinal diseases such as inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), celiac disease and infectious enterocolitis. The specialized junctional complexes called tight junctions provide the intestinal epithelial barrier function. Loss of tight junction integrity and increased intestinal permeability to macromolecules are associated with the pathogenesis of IBD, IBS and celiac disease. Mucosal protective factors such as growth factors and nutrients preserve the gut barrier integrity and are beneficial in the treatment of various gastrointestinal diseases. L-Glutamine the most abundant amino acid in blood plays a vital role in the maintenance of mucosal integrity. Glutamine is traditionally termed as a nonessential amino acid, is now considered a “conditionally essential” amino acid. Its consumption in small bowel mucosa exceeds the rate of production during catabolic stress such as trauma, sepsis and post surgery [1, 2]. In the small bowel mucosa, glutamine is an unique nutrient providing fuel for metabolism, regulating cell proliferation, repair and maintaining the gut barrier functions [3]. The focus of this article is on the role of L-glutamine in the preservation of gut barrier function and the epithelial tight junction integrity and gut barrier function.