The aim of this paper is to develop a reliable and valid tool to assess ethical decision-making ability of nursing students using rubrics. A proposed ethical decision making process, from reviewing related literature was used as a framework for developing the rubrics. Participants included purposive sample of 86 nursing students from the Royal Thai Army Nursing College, experts in measuring and evaluation, and experts in nursing ethics, in Thailand. The results from the study showed that the content validity of the rubrics was adequate, 47 out of 48 scoring rubrics criteria had satisfied IOC's indexes over 0.5. Internal consistency using Cronbach's alpha coefficients was 0.865. Inter-rater reliabilities were between 0.804 and 0.903, intra-rater reliability was 0.948. (Contains 2 tables.)