Students' understanding of negative integers is an important aspect of learning mathematics as it is a requirement for learning broader mathematical concepts. The purpose of this research is to explore students' initial perceptions in understanding negative integers on a number line. This descriptive exploratory qualitative research was conducted on fifth grade elementary school students. The subjects were selected based on students' initial perceptions of writing negative integers on a number line before the teacher presented the material. Students' initial perceptions can be seen from the exploration results of their thinking abilities. The data of this research was collected through written tests and interviews. From the exploration results of research subjects, it was found that there were three characteristics of students' thinking perceptions in understanding the concept of negative integers. These three characteristics are: assume there are no negative numbers; unary understanding; and pseudo understanding. From these findings, it is necessary to design learning which provide scaffolding for students to avoid errors in understanding whole numbers.