The purpose of this study was to investigate the development of pre-service chemistry teachers' (PCTs') argumentation skills in a laboratory course throughout a semester. A case study design was utilised. A total of six PCTs participated in the study. To investigate the development of PCTs' argumentation skills, the laboratory reports that were in the form of science writing heuristic and pre and post semi-structured interviews were employed. Results showed that PCTs' argumentation skills developed over time as they started to generate more powerful arguments which also included deeper conceptual knowledge during the argumentation-based laboratory. The other result of the study revealed that PCTs become successful in explaining chemistry concepts at the sub-microscopic level throughout the course.