question: AIMS AND OBJECTIVES: The purpose of this study was to report the psychometric properties, including validity and reliability, of the decision fatigue scale (DFS). BACKGROUND: Decision fatigue may impair nurses’ ability to make sound clinical decisions and negatively impact patient care. Given the negative impact of the COVID‐19 pandemic on psychological well‐being and the workplace environment, decision fatigue may be even more apparent among clinical nurses. Valid assessment of this condition among clinical nurses may inform supportive interventions to mitigate the negative sequelae associated with states of decision fatigue. DESIGN: This study was a secondary analysis of a parent study using a cross‐sectional descriptive design. METHODS: A convenience sample of 160 staff nurses was recruited online from across the United States. Participants completed a demographic questionnaire and subjective measures of decision fatigue, nursing practice environment scale and traumatic stress. Exploratory factor analysis (EFA), correlation coefficients and internal consistency reliability coefficients were computed to examine the DFS’s validity and reliability within this sample. RESULTS: The EFA yielded a single factor, 9‐item version of the DFS. The DFS scores were strongly correlated with traumatic stress and moderately correlated with the nursing practice environment, and the scale displayed appropriate internal consistency. CONCLUSIONS: This is the first known study to provide evidence of the DFS’s validity and reliability in a sample of registered nurses working during the COVID‐19 pandemic. The results of this study provide evidence of a reliable and valid assessment instrument for decision fatigue that can be used to measure the burden of decision‐making among registered nurses. RELEVANCE TO CLINICAL PRACTICE: Given the relationship between traumatic stress and the nursing work environment, decision fatigue may be a modifiable target for interventions that can enhance the quality of decision‐making among clinical nurses.