Introduction It is important to understand the experiences of elderly people with dementia and their family caregivers. Moreover, the maintenance of family caregivers’ satisfaction with co-occupation is important to ensure that they intend to continue providing care. This study developed and validated the Measure of Supporting Co-occupation, which assesses co-occupation involving elderly people with dementia and their family caregivers. Method This study used a cross-sectional design and questionnaire survey. Participants were recruited from 21 institutions. Descriptive statistics were calculated for the following domains: ‘evocation of the story of co-occupation’, ‘intention to continue co-occupation’ and ‘preferred co-occupation’. The construct validity and reliability of the ‘intention to continue co-occupation’ domain were examined using exploratory factor analysis, confirmatory factor analysis and Cronbach’s alpha. The criterion-related validity of the ‘intention to continue co-occupation’ was examined by means of correlations with other scales. Results There were 115 pairs of participants. Good criterion-related validity and internal consistency were confirmed for the ‘intention to continue co-occupation’ domain. However, confirmatory factor analysis showed insufficient model fitness. Conclusion The ‘intention to continue co-occupation’ domain is not ready for clinical application due to insufficient model fitness, it is necessary to revise the Measure of Supporting Co-occupation.