This study aimed to produce learning trajectory that can help students in learning fractions by using swimming context. The study involved 37 fourth grade students with different capabilities in Elementary School IBA, South Sumatra, Indonesia. This study used an instructional theory called Indonesian version of Realistic Mathematics Education (PMRI). This research used design research method with three stages: preliminary design, the design experiment, and retrospective analysis. Several techniques used for collecting data including a video recording of students interaction in the group discussion, students’ work, and interviewing the students. To conclude, the swimming context could stimulate students’ informal knowledge about the meaning of fractions in which it can be used in the additional learning either the same denominator or different denominator.