The issue of primacy divides Roman Catholic (RCC) and Serbian Orthodox Church (SOC) in theological field. Painful historical heritage from Second World War is also the great obstacle. Yugoslav atheistic state supported development of inter-church relations in acceptable proportion that would increase national relations in Yugoslav federation. Its fear was related to possible 'common front' against ideological system. Regional inter-church relations were initiated by Vatican and Pope Paul II, while SOC accepted it particularly in the social field. Both agreed on common responsibility for the evangelization an atheistic society. The variety of institutional forms of cooperation was also agreed, Common Commission for dialogue of SOC Council and Yugoslav Bishop Conference, and Theological Faculties Conferences in Post World War II Vatican period. In post-conflict Balkan Societies, RCC and SOC agreed to continue common activities for post-conflict rehabilitation and evangelizational purposes.