Recently, the Treaty of Lisbon opened the door for the inclusion of subnational parliaments in the EU decision-making processes. Yet, authors have so far mainly focused on the involvement of national parliaments to the European Union whereas only a few studies dedicated attention to the adaptation of subnational parliaments to European integration. This paper fills that gap by analysing, in a comparative perspective, the involvement of Belgian regional parliamentarians (RMPs) in EU affairs. Following the ‘in foro interno, in foro externo’ principle, Belgian regions are now responsible to conduct foreign policy (including EU affairs) for areas of their competency. Consequently, the scrutiny of EU affairs should not only take place in the national parliament, but should also trigger attention in regional assemblies. By analysing the level of information of RMPs, their perceived impact on EU decision-making processes and their contacts with the executive and other legislative actors in Belgium and in the EU, this paper aims at understanding to what extent and how Belgian regional parliamentarians scrutinize their executives’ EU policies. This paper presents original empirical data collected by an online survey in all three Belgian regional parliaments (Flemish, Walloon and Brussels parliaments) during the winter 2016. The questionnaire is based on a previous survey conducted in Germany (Schneider et al. 2014), and adapted to the Belgian context, which allows for to compare between Belgian and German regional parliaments regional parliamentarians.