<p>This paper investigates how institutional characteristics influence the relationship between board interlocks and corporate social responsibility (CSR). Our findings indicate that the impact of board connectedness on CSR is significantly shaped by institutional ownership characteristics. Specifically, the positive effect of board connectedness on CSR, as documented in prior studies, is primarily driven by institutional investors with diversified portfolios, including transient and quasi-index institutions, as well as independent institutions such as mutual funds and investment companies. Conversely, firms with institutional holdings characterized by concentrated portfolios, such as dedicated or grey institutions, exhibit a weaker association between board connectedness and CSR. Moreover, we find that institutional ownership moderates the relationship between board connectedness and CSR only in manufacturing and high-competition industries through stronger oversight, but not in non-manufacturing or low-competition sectors. These results highlight the pivotal role institutional characteristics play in determining the effectiveness of board interlocks.</p>