Background: Quality of life (QOL) improvement is the main objective of treating patients with irritable bowel syndrome (IBS). This study aimed to assess the validity, reliability, and factor analysis of IBS-QOL-34 questionnaire as a common transcultural instrument for Iranian IBS patients. Materials and Methods: Two hundred and forty patients with IBS (based on gastroenterologists' diagnosis according to ROM III criteria) were referred to Digestive Health Clinic in Psychosomatic Research Center have been selected in this study. Aside with IBS-QOL-34, MOS 36-item short-form health survey (SF-36) and IBS severity index (IBSSI) questionnaires were completed by the cases for determination of correlation coefficients; the data were analyzed using descriptive statistics, factor analysis, Cronbach's alpha, Pearson correlation coefficient by Statistical Package for Social Sciences (SPSS) software, version 18. Results: Total reliability of the questionnaire was reported by using Cronbach's alpha as 0.95, ranging from 0.65 to 0.90. Correlation coefficients of concurrent implementation of IBS-QOL with SF-36 and IBSSI resulted in - 0.61 and 0.64, respectively. Exploratory factor analysis using varimax rotation identified eight principle components, which will determine QOL at 67% variance. Conclusion: According to the results, IBS-QOL-34 questionnaire has good psychometric properties in the research community and can be safely used as a valid tool to assess QOL of patients with IBS for healthcare and therapeutic purposes.