Changes in social systems demonstrate that various structural disadvantages have jointly led to increasing competition among higher education institutions (HEIs) in many countries, especially Taiwan. Institutional administrators must recognize the need to understand how to improve performance and consistently outperform other institutions. Building on two theoretical frameworks that link antecedents and institutional performance, this study examines the relationships among institutional resources, social capital, and performance within Taiwan’s HEIs and the mediating role of institutional resources. By using structural equation modeling (SEM), we tested the multi-group model in three diverse HEI sizes: large, medium, and small. The results showed that each higher education institution, as a function of its history and past success, had different slack resources available, and these resource combinations were shown to be a relevant factor in explaining inter-higher-education-institution variance in each outcome. Considering HEI sizes, even small HEIs can enhance their performance through consolidating existing internal social capital and strengthening external social capital.