Irritable bowel syndrome (IBS) is a common gut-brain interaction disorder. The etiology of IBS is not entirely elucidated, however, among the risk factors, dietary factors are regarded as crucial. Previous studies have primarily investigated the association of single nutrients and food groups with odds of IBS, rather than diet quality, which considers the interaction of food groups in odds of disease. Thus, the current study sought to investigate the association of dietary quality index-international (DQI-I) and odds of IBS in Iranian adults. In this case-control study, dietary intakes of 100 IBS cases and 310 healthy controls were examined using a validated Dish-based Semi-quantitative Food Frequency Questionnaire (DS-FFQ). DQI-I score was then calculated based and categorized into tertiles. The Persian version of the Rome IV questionnaire was utilized to assess IBS. Multivariable logistic regression was used to assess the association of DQI-I score and the odds of IBS. After controlling for potential confounders, no significant association was shown between DQI-I scores and IBS odds among whole and gender-stratified groups. Although DQI-I represents a healthy diet, the results of the current case-control study demonstrated that, a higher DQI-I score was not associated with reduced odds of IBS in fully adjusted regression models. Considering inherent limitations as well as the scarce evidence regarding the association between DQI-I and odds of IBS, further large-scale, prospective studies are required to confirm our findings.