Background Developing confident capacity for ethical decision-making is vital in nursing education. However, no tool examines nursing students’ competence in ethical decision-making. Aim This study aimed to develop an Ethical Decision-Making Competence Scale (EDM-CS) to assess ethical care decision-making competencies in nursing students. Participants and research context Original items were obtained by employing a focus group and the Delphi method. A cross-sectional design was used to confirm the items remained on the scale. Additionally, the scale’s reliability and validity were assessed. (...) The EDM-CS was completed by 498 nursing students. An exploratory factor analysis (EFA) was used to examine the factor structure based on data from group 1 ( n = 250). A second-order confirmatory factor analysis (CFA) was used to examine the model’s fitness based on data from group 2 ( n = 248). This study was conducted between August 2022 and July 2023. Ethical considerations The Institutional Review Board of Chung Shan Medical University Hospital approved this study’s design and procedure. Results From the original 34 items, nine were deleted in the EFA. Thus, the EDM-CS had 25 items and a four-factor structure (ethical judgement, ethical sensitivity, ethical motivation, and ethical action), which explained 60.97% of the total variance. A second-order CFA identified a second-order factor termed ‘ethical decision-making competence’ with 18 items (root mean square residual = 0.052). The EDM-CS scores correlated significantly and positively with the scores on the Scale of Protective Factor-24 (r = 0.47, p <.001), which indicated good convergent validity. Cronbach’s alpha coefficient of the final EDM-CS was 0.90 and ranged from 0.73 to 0.80 for the four subscales. Discussion and conclusion The EDM-CS was validated to fit the data adequately. It can be used to evaluate clinical nursing students’ ethical decision-making abilities and to develop education strategies to improve their ethical care competence. (shrink)