This study examines the relationship between ethnic diversity on corporate boards and corporate investment efficiency within South African firms listed on the Johannesburg Stock Exchange from 2011 to 2024. The findings reveal that firms with a higher proportion of ethnically diverse directors reduce investment inefficiency. These results strengthen the literature around the significant influence of board diversity on financial decision-making and imply that greater ethnic representation can enhance investment strategies. These results were also tested for any endogeneity issues and robustness tests. The research holds practical and policy relevance, advocating for governance frameworks that strategically incorporate ethnic diversity. As one of the first studies to explore this relationship in the South African context, it offers valuable insights into how board composition can shape corporate financial behaviour.