The purpose of this study is to determine the experience of mathematics preservice teachers related to function and equation concepts and the relations between them. Determining preservice mathematics teachers’ understanding of function and equation concepts has great importance since it directly affects their future teaching careers. Data were collected by a questionnaire and semi-structured interviews and analyzed using existential- phenomenology. The results show that the experiences of preservice math teachers related to these concepts can be summarized under six different titles, namely, confusion of the definition of function with one-to-one and onto properties, relating it with daily life (exampling), failure to take the functioning conditions into account, the relation between the values which make the function zero and roots of the equation, multiple representations of functions and taking the defining set of functions and equations into account.