The article is devoted to the analysis of the factors of decentralization in Spain on the example of the Basque Country. Particular attention is paid to the factor of European integration and the EU regional policy in the political development of Spain. The purpose of this article is to consider the resources for decentralization in Spain with a focus on European integration (in particular, the EU regional policy). The first part of the article proposes a research methodology. The second examines some of the factors of decentralization offered by the scientific literature. The third part of the article reveals the features of the «three-tier» model of regional policy in Spain and the indicators of the EU regional policy effectiveness. The fourth part examines the experience of the Basque Country in the European integration, in particular, the EU's regional policy. Referring to the database of the «Manifesto» project, the author comes to the conclusion that connection between the processes of decentralization in the Basque Country and European integration can be manifested in the texts of the electoral programs of the Basque Nationalist Party. The scientific significance of the article is to analyze the impact of European integration on the processes of decentralization in Spain via the data of the «Manifesto» project.