During the last few decades, it is almost impossible to envision political system of European countries without the political parties. Of course, because of that, political parties have also been important actors during the process of European integration. Furthermore, once they started cooperating on the European level in the EU institutions, it was clear that a lot of European parties have plenty of things in common when it comes to programmes and ideologies. Therefore, the uniting of those parties began and today one of the pillars of EU’s political system are European political parties. However, because the EU is enlarging itself constantly since its inception, the influx of new member states has had an impact on many sectors of the Union – including the European political parties themselves. In this paper, the focus of analysis is on the impacts of the EU enlargement on European political parties and their political groups in the EP in three ways: internal structure and organisation, ideology, and inner cohesion. The Europarties analysed were EPP, PES/S&D, and ALDE/Renew. EU enlargement has mainly impacted the Europarties in a positive way. The impacts were mainly organisational – the influx in the number of member parties basically forced the political families to reform their internal structure in order to become more efficient. Ideologically, the high number of new members from Central and Eastern Europe has not changed the general ideological course of the parties. Moreover, they became stronger and more united. When it comes to voting process in the EP, the European political groups remained impressively united and disciplined despite the worrying thoughts before the enlargement wave in 2004. The European parties not only remain organisationally cohesive and united despite their growth in the number of new party members, but they became even more structured and internally strong by reforming the most important inner-party bodies.