The accession of the Republic of Croatia to the full EU membership has placed before the Customs Administration a series of tasks to be fulfilled in order to successfully respond to business challenges in a single market. This included the full incorporation of the acquis communautaire with the aim of harmonizing and simplifying customs and excise formalities, which also brought about the need to adapt and modernize the Customs Administration's business systems. For this research, there is a problem in the sense of the unknown effects of the Customs Administration's restructuring at the accession of the Republic of Croatia to the European Union. Accordingly, a study has been carried out with the aim of detecting these effects at the beginning of the action on the single market of the European Union. For the purpose of facilitating the achievement of the main objective, the auxiliary objectives and research problems are set out to address this work. In order to fulfill the objective of the research, it is necessary to explore literature in the field of organization, change management and strategic management. In addition, for the purpose of achieving the goal of the work, it is necessary to collect and explore all available data related to the research problem. In this paper all relevant data are processed by methods of analysis and synthesis, descriptions, comparisons and deductions. Part of the data was collected by interview method. The research accomplished the goal and also gave answers to the research questions. The effects of the above mentioned restructuring of the Customs Administration have been successfully identified. The elaboration of the essentially fragmented form of organizational structure, the adaptation of the legislative framework of the European Union, the introduction of new information and communication technologies with the adequate management of human resources gave a completely new look to the Customs Administration. The same has, with effective implementation of the set of activities, transformed from the administrative institution a completely new form of effective public service for citizens and the economy.