Oral glutamine supplementation is highly effective in preventing and delaying radiation-induced esophagitis, one of the most common discomforting side effects of radiation to the thoracic area among lung cancer patients. According to the literature, lung cancer is the leading cause of death among all cancers with the highest incidence worldwide. This paper aims to emphasize the importance of oral glutamine supplemen- tation in preventing radiation-induced esophagitis among lung cancer patients. Several databases have been searched and seven studies included in this review (five randomized control studies, one quasi-experimental study and one systematic review) with a total of 453 patients. The patients in these studies were diagnosed with lung cancer regardless of type or stage. The patients were either assigned to an intervention group (glutamine supplementation) or a control group. These studies were conducted in the US, Turkey, Spain, and Greece from 2003 until 2012. The results showed that 10 mg of oral glutamine three times per day on a daily basis (from one month before starting radiation until one month after completion of radiation)was effective in preventing and delaying radiation-induced esophagitis.