ABSTRACT: This study investigated the effect of board characteristics on the financial performance of companies listed on the Nairobi Securities Exchange (NSE), with firm size examined as a potential moderating factor. The specific objectives of the study were to determine the effect of board size on the financial performance of companies listed on the Nairobi Securities Exchange, to assess the influence of board diversity on the financial performance of companies listed on the Nairobi Securities Exchange, to examine the influence of board committees on the financial performance of companies listed on the Nairobi Securities Exchange, to evaluate the impact of board independence on the financial performance of companies listed on the Nairobi Securities Exchange, and to determine the effect of board expertise on the financial performance of companies listed on the Nairobi Securities Exchange. The study was grounded in agency theory, resource dependence theory, and stewardship theory. The study adopted a cross-sectional research design and a quantitative methodology. Secondary data from the 2020–2024 annual reports of all listed companies on the NSE were analyzed using panel regression techniques. The random effects model results indicated that model was statistically significant (Wald χ² = 52.16, p = 0.0021 < 0.05) and explained 50.19% (R² = 0.5019) of the variation in financial performance. The findings showed that board size had a positive and significant effect on financial performance (β = 0.3056, p = 0.000 < 0.05). Similarly, board independence was positively and significantly associated with ROA (β = 0.5312, p = 0.001 < 0.05). In addition, board expertise had a strong positive and significant effect on financial performance (β = 0.4119, p = 0.000 < 0.05). The results further revealed that board diversity positively and significantly influenced financial performance (β = 0.3307, p = 0.000 < 0.05). Likewise, board committees had a positive and significant effect on ROA (β = 0.5421, p = 0.008 < 0.05). The study recommends that firms listed on the Nairobi Securities Exchange strengthen their corporate governance structures by optimizing board composition in terms of size, independence, expertise, diversity, and committee effectiveness, as these were found to significantly enhance financial performance.