The aim of this study is to investigate pre-service teachers’ subject matter knowledge of probability, within the scope of conceptual and procedural knowledge. This case study, was carried out with four pre-service primary school mathematics teachers selected according to the critical case sample. To determine the pre-service teachers’ knowledge of probability, firstly they were requested to answer the question form composed of six questions. After this process, obtaining in-depth information about their knowledge of the basic topics of probability was aimed with clinical interviews. As a result of the data analysis, it was seen that although the pre-service teachers had moderate and high level of procedural knowledge about probability, there were many deficiencies in the conceptual aspect and they could not explain why they solved the questions that they responded procedurally. Besides, it has been determined that pre-service teachers conceptualprocedural knowledge were not very balanced, and their conceptual knowledge was less adequate than their procedural knowledge. Research findings suggested that contents in undergraduate probability courses may include conceptual knowledge along with procedurel knowledge