This study examines how generational succession in family firms influences ESG greenwashing, a critical yet underexplored issue in sustainable governance. Using a multi-period difference-in-differences (DID) model and data from Chinese listed family firms (2012–2022), we demonstrate that generational succession significantly exacerbates ESG greenwashing behaviors. Notably, the succession duration negatively moderates the impact of generational succession on ESG greenwashing. Robustness checks confirm the reliability of these findings: the baseline results remain consistent after addressing endogeneity through propensity score matching (PSM) and employing alternative measures of the dependent variable. Heterogeneity analysis further reveals significant variations across family governance models and industry characteristics. Directly established family firms and those in non-manufacturing sectors demonstrate higher propensities for ESG greenwashing post-succession compared to inherited or manufacturing-oriented enterprises. These findings contribute to the literature on family business governance by linking intergenerational dynamics to strategic ESG manipulation, offering novel insights into the dark side of succession in sustainability contexts. The study also provides practical implications for policymakers and regulators to mitigate greenwashing risks during critical governance transitions.