The aim of this study is to explore the probability-related pedagogical content knowledge (PCK) of secondary school mathematics teachers in terms of content knowledge, curriculum knowledge, student knowledge, and knowledge of teaching methods and strategies. Case study design, a qualitative research model, was used in the study, and the participants were three secondary school mathematics teachers. Data collected via observations and semi-structured interviews were analyzed using a deductive approach. Findings indicate that the PCK of these secondary school mathematics teachers about probability is insufficient; furthermore, teachers' beliefs were the most important factors impacting their PCK. In addition, one of the results is that professional experience has a partial effect on PCK.