Research study on students' conceptions of irrational numbers upon entering university is of importance towards the transition to university. In this paper, we analyze students' conceptions of irrational numbers using their representation as non-repeating infinite decimals. The majority of students in the study identify the set of all decimals (finite and infinite) with the set of rational numbers. In spite of the fact that around 80% of the students claimed that they had learned about irrational numbers, only a small percentage of students (19%) showed awareness of the existence of non-repeating infinite decimals.