In this study the aim was to investigate the development of Pedagogical Content Knowledge (PCK) of early career chemistry teachers. Two pre-service chemistry teachers were followed during a one-semester course and after a three-year period as formal high school teachers. The data involved teachers´ writings, recordings of lessons and reflections during the course. After three years, the same content lessons in an actual school environment were videotaped. The teachers were then interviewed using the videotapes for stimulated recall. The instruments Content Representation (CoRe) and Pedagogical and Professional-experience Repertoires (PaP-eR´s) were used to document and to describe teachers’ PCK. Analysis of discursive interaction patterns was performed during lessons. Data analysis was based on the components of teacher knowledge as described in the Morine-Dershimer Model. The development of PCK was enhanced during the pre-service teacher education through the experiences of planning and conducting interventions in the classroom and particularly during the reflection-on-action activities. Results after three years of professional experience revealed an improvement in these teachers’ PCK and highlighted the central role of the reflection process and practical experience. From the analysis carried out, it emphasized the need to act in these early years of professional experience through collaborative groups, supporting the reflection process and aiming to contribute more directly to the development of teachers' PCK.