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This is a descriptive research with qualitative approach. It purpose is to know the conceptual understanding mathematics in high school students based on cognitive reflective-impulsive style in matrix material. The data were collected in cognitive reflective and impulse style high school students of class XI. Data for this study were collected using tests, interviews and documentation. Data reduction, display and verification were used to analyze the data. Using triangulation technique, the data analyze concluded that the mathematics conceptual understanding of cognitive reflective style is higher, especially in two indicators, they are restate the mathematical concepts and connect it to the various concepts in mathematics and non-mathematics. The subject of cognitive reflective and impulsive style have the same tendency in mathematical conceptual understanding especially in some indicators, they are identify the characteristic of procedure or concept, give examples or counter examples of the learned concepts and present it in various forms of mathematical representation (tables, graphs, diagrams, sketches, mathematical model, etc). Based on the analysis, it can be concluded that the subject of cognitive reflective style has higher mathematical conceptual understanding. Keywords: Analysis, Mathematical Conceptual Understanding, Reflective-Impulsive