Background: Thailand’s population is currently the third most rapidly aging in the world, with an estimated 20 million ageing population by 2050. Sustainability of the family based long-term care model is challenged by the chronic burden on family caregivers and by smaller family sizes. We aimed to introduce a new service model, Community Integrated Intermediary Care (CIIC), TCTR20190412004, including free of charge intermediary care services at CIIC centers in the local community, to help older adults whose caregivers are temporarily unable to sustain care at home. Since Thai society upholds values of gratefulness, it is better to estimate willingness to use such an intermediary care service first, before introducing the service. Methods: A total of 867 pairs of senior citizens and their family caregivers were interviewed with structured-questionnaires in 2019. Descriptive analysis and binary logistic regression were applied to determine the predictors of family caregivers’ willingness to use the CIIC service, guided by Anderson’s model of health services use. Results: About 26.8% of elderly participants and 24.0% of family caregivers were willing to use an intermediary care service. The family caregiver determinants of predisposing factors (kinship: spouse caregivers, other relatives, maid or friends; job types: own business and private company staff), enabling factors (original community residents and monthly income ≤9000 baht), and need factors (caregiver burden total scores ≥24, taking leave for caregiving, and having diabetes), were found to be significantly associated with willingness to use the CIIC service. Conclusions: The baseline survey data noted that caregivers’ sociodemographic factors and burden determined their willingness to use the intermediary care service, although the dependency of care recipients was low in this study. This, nonetheless, indicated that there is need for a backup respite care to strengthen current family based long-term aging care in Thailand.