Construction of the mathematical concept is important to support students' success in learning. Factorization is one of the important subjects to be mastered by students in order to solve advanced mathematics problems. Reflective abstraction is a mental mechanism which someone can build all mathematical concepts at all levels. This study used the mental structure of APOS theory (Action, Process, Object, Schema) to describe the mental mechanisms of interiorization, encapsulation, and thematization. This study aims to reveal and describe the reflective abstraction of students in reconstructing the factorization concept. The results obtained that female student at the action stage connected the mathematics knowledge that belongs to the factorization content to find the answer. In the process stage, she could explain how she got the answer. In the object stage, she could explain the rules used. In scheme stage, she could connected the actions, processes, objects, and schemes that have been formed to form a factorization scheme and she could do more complex tasks, while male student only reach the process phase. Therefore, the reflective abstraction of female student is better than male student with medium mathematics ability in reconstructing the factorization concept.