Attribution theory deals with the question of how individuals make judgments and seek to explain how they consider the causes of their behaviours and those of others. Attributions have the potential to affect beliefs, emotions and behaviour. Therefore, attribution theory has significantly contributed to the studies on motivation. This study examined student teachers' causal attributions for success and failure in mathematics. The participants in this study were 28 student teachers in the department of secondary school mathematics education at a public university in the north of Turkey. To collect data, a questionnaire composed of one open-ended question was administered to the student teachers and they were asked to write their opinion about the causes of a student's failure and success in mathematics. Student teachers wrote and submitted a reflection of one or two pages. Their written responses were examined and qualitatively analysed to determine the common themes by means of qualitative analysis software. The results have revealed that the student teachers categorize four causes to attribute for the students' failure in mathematics: causes originating from students, causes originating from teaching and learning methods, causes originating due to the nature of mathematics itself and physical causes. The most frequent cause mentioned by the student teachers was innate math talent, an internal, stable and uncontrollable cause.