Urban regeneration involves a highly contested process of social transformation. Examples from China have shown that this process has led to poor social sustainability. Previous studies have not adequately addressed the issue of poor social sustainability. This study aims to address this gap by developing a set of valid and reliable performance indicators for assessing the social sustainability of urban regeneration initiatives in China's Historic Urban Areas (HUAs). Through an extensive literature review and a Delphi survey, critical social sustainability factors facilitating urban regeneration were identified. An assessment tool was subsequently proposed, comprising eight themes, 29 indicators, and a corresponding point-scoring system. Finally, Xi'an was selected as a case study to apply and test the applicability of the tool and to evaluate social sustainability performance to further explore improvement strategies. The results show that adequate housing, housing quality, participation in regeneration initiatives, and safe design were the most critical indicators determining the social sustainability of urban regeneration. Additionally, the results reveal indicators with limited contribution to achieving social sustainability in Xi'an. The research findings have policy implications for pushing socially sustainable urban regeneration initiatives in China.