Representation is an important aspect of learners in building a relational understanding of mathematical concepts. But the ability of a mathematical representation of students in building relational understanding is still very limited. The purpose of this research is to description of mathematical representation of students who appear in building relational understanding on concept of area and perimeter of a rectangle. This research is a case study. The research instrument is tests and interviews. The participants in this study were Grade seven students. Two students are selected based on the characterization of the mathematical representations that appear. The study results a visual and symbolic representation used by students in building relational understanding on the concept of area and perimeter of a rectangle. Visual and symbolic representation suggests students to build relational understanding.