The concept of fractions given in learning is the concept of part of whole and part of unit. The development of student's concepts of fractions can be built through fraction schemes. A partitive fraction scheme is a scheme that estimates the size of the fraction in the form of non-units to the whole that is not partitioned. The concept of fractions using a partitive fraction scheme uses a strong understanding of the concept of the part unit and part-whole fractions. This study aims to photograph the process of developing students' mental actions in constructing the concept of fractions using a partitive fraction scheme. This research method uses a qualitative approach with a case study type on students who are able to express partitive fraction schemes. The participants of this study were fifth-grade elementary school students who already understood the concept of part-whole and part of unit. The results showed that students used two types of mental action processes in the partitive fraction scheme: direct and indirect.