Objectives: This study aimed to evaluate nursing students’ knowledge, attitudes, and self-efficacy regarding chemical, biological, radiological, and nuclear (CBRN) threats. Methods: A descriptive, cross-sectional design was employed between January and May 2025 with 432 nursing students. Data were collected using an information form, the CBRN Knowledge Test, the CBRN Attitude Scale, and the CBRN Self-Efficacy Scale. Results: The mean scores were 19.47 ± 2.76 for knowledge, 3.59 ± 1.27 for attitude, and 3.44 ± 0.73 for self-efficacy. Female students demonstrated significantly higher knowledge and self-efficacy scores than males (p < 0.005). Knowledge, attitude, and self-efficacy scores differed significantly across academic years (p < 0.001), with fourth-year students showing the highest knowledge levels. Students who had received CBRN training reported higher knowledge and attitude scores (p < 0.001). Similarly, students expressing a desire for CBRN training had significantly higher knowledge, attitude, and self-efficacy scores (p < 0.005). Conclusions: The findings indicate that nursing students have notable gaps in practice-oriented domains such as triage, radiation safety, personal protective equipment use, and decontamination. These results underscore the importance of integrating structured, simulation-based CBRN training into undergraduate nursing education to enhance preparedness and practical competence.