Tehran University of Medical Sciences Nursing Practice Today 2383-1154 0 0 2026 10 31 5686 5686 Fatemeh Pakdin Instructor of Emergency Nursing Department, Master's student of Emergency Nursing, Nursing School, Aja University of Medical Sciences, Tehran, Iran. Zahra Farsi MMedEdu, Ph.D., Professor, Trauma and Surgery Research Center, Aja University of Medical Sciences, Tehran, Iran Reza Momen Ph.D. Student of Nursing, Ph.D. Nursing Department, Nursing School, Aja University of Medical Sciences, Tehran, Iran. 2026 09 10 2026 10 24 Background and Aim: Defibrillator competence requires cognitive and psychomotor skills, but instruments for assessing defibrillator skills are limited. Therefore, this study aimed to develop and evaluate the validity and reliability of a checklist for assessing defibrillator operation skills. Methods and Materials: This methodological study was conducted in 2025–2026 at a Nursing School, in Tehran, Iran. The Defibrillator Operation Skills Assessment Checklist (DOSAC) was developed from the nursing curriculum, literature, 2025 AHA and ERC guidelines, and manufacturer documentation. Content validity was assessed by 10 experts using the Content Validity Ratio (CVR), Item- and Scale-level Content Validity Index (I-CVI and S-CVI), and modified kappa. Face validity was assessed by 15 nursing students and 15 nurses using qualitative assessment and Item Impact Score (IIS), respectively. Inter-rater reliability was evaluated in 20 nursing students assessed by two raters using a two-way random-effects Intraclass Correlation Coefficient (ICC), Cronbach’s alpha, and exact agreement. Results: DOSAC contained 64 items across four scenarios: device preparation and patient monitoring, manual defibrillation, synchronized cardioversion, and AED use. All items met validity criteria. Mean CVR was .909, S-CVI/Ave was .989, modified kappa was .989, and mean IIS was 4.437. Reliability was excellent, with ICC = .986 for the total score, Cronbach’s alpha = .993, Pearson's r = 0.986, and 94.3% exact item agreement. Scenario-level ICCs ranged from .893 to .999 (all p < .001). Conclusion: The DOSAC demonstrated strong content validity and excellent reliability and may provide a standardized tool for assessment of defibrillator operation skills in nursing education and practice. https://npt.tums.ac.ir/index.php/npt/article/view/5686