The United Nations continues to raise controversy, also in its capacity as a peacekeeping institution. A number of studies have reported serious abuses committed by peacekeeping personnel in the host countries, abuses that are contrary to the UN peacekeeping mission. This paper seeks to trace back the philosophical origins on which the ethical code of the UN peacekeepers is based. It is argued that the source of moral guidelines and duties for the UN peacekeepers is provided by human rights as captured by the Universal Declaration of Human Rights. The rationale of the human rights is in turn founded on the philosophy of Immanuel Kant. The latter has emerged as a part of Enlightenment tradition which has rejected Aristotelian view of the human condition, in particular Aristotelian virtue ethics and moral psychology. The consequences of this theoretical omission are considered in relation to the UN peacekeepers training and their misconduct during their service.