The institutionalisation of party system describes the degree to which politics are rooted in the competition between different political parties. The aim of this article is to analyse the above mentioned rooting on one of the levels of research – during parliamentary elections in Poland – when the parties’ commitment and activity is the most visible and strong. We will try to answer the question whether our political system is institutionalised and if it is, to what degree. We will also try to discuss whether it can be defined as a consolidated party system.