This study aims to reveal science teachers' performances in designing TPACK-based argumentation practices for teaching geology. This study used a holistic single case study design where thirty-two science teachers participated in a professional development program. All materials such as videos, etc. used by the teachers and the Pedagogical Reasoning Assessment Form (PRAF) were used as data collection tools. Descriptive analysis was conducted through the scoring rubric for lesson plans and content analysis for PRAF. Findings indicated that teachers successfully used TPACK indicators in their lessons. Findings also revealed that although teachers thought that formative assessment could be improved by learning from professional development programs, they did not use technology for assessment in their lesson plans. Related to the argumentation process, teachers tended to construct their arguments with one rebuttal, and they could not use warrants. Moreover, although teachers had high scores in the quality of claim, rebuttal, and backing respectively, they had some problems in presenting data and warrant for the claim. PRAF findings indicated that the TPACK-based Argumentation Practices Professional Development Program (TPACK-bAP PDP) enriched their lesson plans in some aspects.