This study proposes and tests a model that integrates ethical leadership, internal social capital, and firm performance in small‐ and medium‐sized family firms at different generational stages. Using the upper echelons theory and the social capital perspective of familiness, this study shows that ethical leadership can explain the effectiveness of certain behaviors in relation to family firm performance. Moreover, social capital helps spread a leader's business ethics to firm members, thus improving the family firm's performance. Our results show that founders' personalities and identities determine high internal social capital, which decreases over generations. The study also shows that internal social capital is a communicative element crucial to ethical leadership, facilitating the absorption of the culture and values of the family in the firm. This powerful resource should be promoted and supported by coherent behavior over time by senior leaders.