Abstract Background & Aim: Ethical reasoning is one of the criteria for professional qualifications of nurses. Promoting the principles of professional performance through emphasis on ethics reinforce the ethical reasoning in nurses. Therefore, this study aimed to evaluate the impact of training on ethical reasoning among nurses. Material & Methods: This study is Quasi-experimental (pretest and posttest control group). The sample consisted of 30 nurses from Shahid madani hospital, Tabriz, Iran in 2014. Participants were selected by convenience sampling and randomly allocated to experimental and control groups (n=15 per group). Moral reasoning questionnaire was administered in both groups before and after intervention. Experimental group met weekly (four 90-minute sessions). The data were analyzed by analysis of covariance using SPSS v.20 software Results: The results of analysis of covariance showed that after intervention, a significant decrease in moral reasoning scores were observed in the experimental group (P = 0/001); so nursing ethics training enhanced moral reasoning significantly in experimental group . Conclusion: Nursing ethics education can increase the nurses' moral reasoning; so this intervention is recommended as an effective program to promote ethical reasoning and its implementation can improve the professional qualifications of nurses.