This paper examines the moderating effect of environmental, social, and governance (ESG) disclosure on the relationship between herd behavior and market capitalization. The financial data of 22 companies listed in the S&P/EGX ESG index from 2018 to 2023 is analyzed using panel data analysis in the study. The empirical results reveal a statistically significant positive association between market capitalization and herding behavior. Furthermore, the results indicate that implementing mandatory ESG disclosure strengthens the association between market capitalization and herding behavior. The analysis demonstrates that companies with superior ESG performance impact firm market capitalization, ultimately leading to higher stock valuations. This emphasizes the growing importance of ESG factors in formulating investment decisions, reinforcing market transparency, and influencing overall market dynamics in Egypt