While nursing is an ethical profession, unethical behavior among nurses is increasing worldwide. This study examined the effects of an ethics seminar on nurses' moral sensitivity and ethical behavior. A total of 37 nurses (17 experimental, 20 control) were recruited. The ethics seminar was held over a 6-month period from May to October, 2018, and comprised six sessions held once a month for two hours. Moral sensitivity and unethical behavior were measured at the start and end of the seminar. Moral sensitivity and unethical behavior showed a negative correlation (r= -.455, p<0.01). After the ethics seminar, the experimental group's moral sensitivity was significantly increased (t = -1.039, p = 0.314). The mean scores of unethical behavior at pre and post-test in the experimental group were 12.59 and 9.47, respectively. This was a statistically significant difference (t = 3.118, p = 0.004). There was no statistically significant difference in the mean score in both moral sensitivity and unethical behavior in the control group. We conclude that ethics seminars can enhance moral sensitivity and reduce the risk of unethical behavior among nurses. Regular ethics seminars and training must be provided to nurses as a matter of policy.