Peacekeeping operations have grown in scope and frequency over the decades since the establishment of the Unite Nations (UN). In particular, the optimism attending the UN’s prospects of greater leadership in conflict resolution in a new season of openness following the end of the Cold War saw increasing UN involvement in varied and complex conflicts – many involving ethnic rivalries that have surfaced amid the turbulence of the formation of new states and the spread of democracy in the last decade. Unfortunately, few of these operations have been widely regarded as successful, and some have ended in absolute disaster. There is a continuing need to search for the factors which hinder success and to evaluate the compatibility of current peacekeeping methods and assumptions with conflicts in which those factors play a significant role. Thus, this paper begins by examining the design, function and doctrine of traditional peacekeeping missions, from which a definition of success is also established. The nature and particular difficulties of ethnicity and ethnic conflict are delineated and a key interaction between these and the current broad UN approach to conflict is explored. From this understanding, two UN missions – the United Nations Operation in Mozambique (ONUMOZ) and the United Nations Assistance Mission for Rwanda (UNAMIR) – are compared to determine whether a substantial ethnic component to a conflict may in fact emerge as a significant hindrance to successful peacekeeping operations given current methods and assumptions. The conclusion drawn is that the success of UN peacekeeping missions, which are designed to facilitate negotiated settlements with the consent of the parties involved, is seriously challenged when the conflict in question is characterized by significant ethnic animosity. It is suggested that UN planners should therefore intervene in ethnic conflict more circumspectly, and that more serious consideration should be given to more robust measures if a peacekeeping mission is undertaken.