The purpose of this research is to determine the conceptual understanding of pre-service science teachers about "Colligative properties", which are aimed to be taught within the scope of Chemistry-II course, within the framework of the argumentation-supported problem based learning (AS-PBL) method. The study, in which 24 pre-service science teachers participated, was conducted as practice-based action research, which is one of the qualitative research methods. The arguments of pre-service science teachers about the related chemistry topic were analysed according to the Walton Argumentation Model (Conclusion-Premise) and were described through content analysis. At the end of the research, it was observed that pre-service science teachers had misconceptions of arguments, which they mostly structured as a "conclusion sentence", about the related chemistry topic before the implications. After the implications, it was observed that the majority of pre-service science teachers showed the ability to present "a conclusion and at least one premise", but the conceptual understanding of all participants did not reach the expected level.