INTRODUCTION: Disaster nursing is a complex, dynamic, and resource-limited working environment, like military operations. As the COVID-19 outbreak has shown, not only hospitals, but all communities need nurses who can systematically respond to disasters. It is important for nurses to possess the necessary readiness to respond to disasters with confidence and autonomy. However, there is a lack of evidence for a theoretical framework for nurses' cognitive readiness for disaster nursing. OBJECTIVE: The purpose of this study was to describe the development of a middle-range theory about nurse's cognitive readiness in disaster response. METHODS: Fletcher and Wind's model was modified to develop a theoretical framework for disaster cognitive readiness by using theory derivation and sentence synthesis. RESULTS: In the developed theory, "Disaster cognitive readiness" refers to the cognitive preparedness of nurses for effectively responding to and managing disaster situations which are in high-stakes, complex environments, achieved through a combination of education, training, and practice in essential skills such as problem-solving, communication, resilience, and ethics. The theory for disaster cognitive readiness described the competencies: knowledge, problem-solving, metacognition, decision-making, adaptability, risk-communication, resilience, and ethics. The outcomes of disaster cognitive readiness are personal (job satisfaction, professional growth) and organizational (disaster management, disaster resilience) outcomes. CONCLUSION: The results of this study are expected to be useful in developing educational and training programs that emphasize the characteristics of disaster nursing competencies and in verifying their effectiveness in enhancing disaster cognitive readiness as well as individual and organizational outcomes.