The World Health Organization emphasizes the importance of providing integrated care for older people. Taiwan is the fastest aging country in the world. In 2016, Taiwan implemented the Long-Term Care Plan 2.0 (TLTCP 2.0), aimed at providing integrated long-term care (LTC) services in communities. However, LTC service agencies have not been able to evaluate the level of integrated care they provide due to the lack of an effective assessment tool. To address this need, this study sets out to develop an integration assessment tool, namely the Self-Assessment for Service Integration in Long-Term Care (SASI-LTC), which will allow LTC agencies to self-evaluate their current level of integration from multiple perspectives. The SASI-LTC was developed based on Evashwick's framework, underwent two rounds of Delphi panels with twenty-six experts, and a pilot test with 243 valid questionnaires from administrators of Tier A agencies who are responsible for integrating LTC. The Delphi experts assessed the content with high levels of agreement using medians, the scale content validity index (SCVI) and item content validity index (ICVI). The SASI-LTC included four domains (inter-entity organization and management, integrated care coordination, integrated resources, and integrated information systems) with thirty items. The SASI-LTC showed good reliability (Cronbach's α = 0.94) and good validity, and a confirmatory factor analysis showed a good model fit index [χ2/df = 1.38; RMSEA = 0.040; CFI = 0.963; SRMR = 0.049] in pilot testing. While the SASI-LTC is a useful and feasible tool for Taiwan's LTC service agencies to evaluate their level of integration in providing LTC services, it could also be used in other countries with minor adjustments to localization of items related to financial integration.