Objectives: This study aimed to develop a scale that can measure the role competency of oncology nurses during shared decision-making process. Methods: A total of 226 oncology nurses who actively provide direct care to patients from inpatient and outpatient oncology units in the Midwest and Pacific Northwest completed the online or mail survey. Exploratory factor analysis and parallel analysis showed the multidimensionality of the role competency scale on shared decision-making nurses. Results: The role competency scale on shared decision-making nurses revealed four dimensions: knowledge, attitudes, communication, and adaptability. The 22 items have excellent internal consistency with a Cronbach’s alpha of 0.91. The four subscales also have adequate reliability with Cronbach’s alpha >0.70 as well as greater than 0.70 Spearman–Brown’s correlation coefficients in split-half reliability testing for each subscale. Conclusion: The new scale has the potential to be used as a clinical tool to assess the need for shared decision-making education and training in oncology nurses.