Purpose The objective of the research is to examine the effect of the capital structure flexibility on firm survival by using the secondary financial data of SET50 in Security Exchange in Thailand (SET) between 2010 to 2021. Theoretical Framework This research originally uses the Modigliani and Miller (M&M) theory of capital structure and its application from modern capital structure theories to explain the conceptual framework. These modern capital structure theories include the trade-off theory, the packing order theory, the market timing theory, the agency theory and the stakeholder co-investment theory.