Debates around sound corporate governance propose board diversity as a key attribute to sufficiently challenge executive management for stakeholder engagement. This study contributes to this debate by empirically investigating the effect of board diversity on corporate social disclosure (CSD) of Vietnamese listed firms. The study finds a significantly positive effect of diversity-in-boards (dissimilarities among directors within a board, i.e., demographic attributes of board members) on CSD while diversity-of-boards (dissimilarities among firm boards, i.e., board structure) has no effect on CSD. The results contribute by showing that a single theoretical approach can provide an adequate explanation for board diversity. The study contributes methodologically by demonstrating the design and measurement of board diversity indices, and a three-dimensional stakeholder-relevant CSD index. The findings benefit regulators and corporate executives in better understanding firms’ CSD practices and stakeholders’ expectations.