It has been demonstrated that in most of the countries electoral behaviour follows a pattern of nationalization, that is, national politics substitute local politics (Caramani 2004, Alemán and Kellam 2008). Most of the researches (both the comparative and the single case-study ones) analyse the phenomenon of nationalization and its strength by focusing on a single type of election: the legislative/parliamentary. When dealing with comparative researches, this also implies that the electoral offer and the analysed context differ from one country/within-country area to another. The original contribution of our paper to the debate on the nationalization of electoral behaviour consists in offering both a new methodological and substantive perspective. From a methodological point of view, we propose a quasi-experimental design. The nationalization will be measured for two types of elections (presidential and legislative), in the same country (France), at the same territorial level (departments), for a span of time indented to cover the period of the Fifth Republic, and employing nine presidential and fourteen legislative elections. For this analysis, the nationalization of the electoral behaviours will be calculated by employing first the standard deviation, the Mean of Absolute Deviation (Rose and Urwin 1975) and then the Bochsler index (2010). The Bochsler index allows measuring the nationalization at the country level, and it was conceived not to be sensitive to the size and the number of parties. Therefore, the Bochsler index is the best instrument when dealing with a comparative or a longitudinal design. From a substantive point of view, this paper aims to demonstrate that the degree of nationalization depends on the type of election. In our case, which is a semi-presidential system, we expect to observe a higher degree of nationalization in the presidential elections compared to the legislative elections. In fact, with regard to the legislative elections the local dimension of the vote (department level) should lead to a higher fragmentation of the electoral behaviour.