We examined the feasibility of using the Japanese version of the Mental Health Continuum Short Form (MHC-SF-J) index as a mental well-being measure in patient-reported outcomes. We targeted patients with inflammatory bowel disease (IBD) as the study group. We used a web-based questionnaire to measure the MHC-SF-J index and, confirmatory factor analysis was used to assess goodness of fit, evaluating reliability and validity in comparison with healthy participants aged ≥60 years. The results of the confirmatory factor analysis showed that the reliability and validity of the second-order, three-factor model were high in comparison with those of the analysis results of healthy participants aged ≥60 years. Among the 557 participants (65.7% men, average age 52.7 years; 34.3% women, average age 45.6 years), the response rate was 100% and the continuation rate was 99.8%. The mean value of the MHC-SF-J index was 23.4 points (of a total score of 70 points). Overall, the MHC-SF-J index evaluated in this study is feasible for electronic patient-reported out-comes in patients with IBD.