In Mathematics learning, justification is an important component for building students' skills in mathematical reasoning, understanding concepts and mathematical communication. Justification is the process of proving the truth of a mathematical statement by giving reasons based on definition and previously proven property, theorem or lemma.

During the learning process takes place, each individual has different ways or characteristics that cause differences in the ability to reason, understand, and communicate in receiving and processing information. The difference is possible because of the different learning styles of each student. This study aims to obtain a natural description of mathematical justification of junior high school students in a quadrilateral material in terms of Kolb learning style. This research is a qualitative descriptive research using questionnaire method and task-based interview.

The subjects of this study consist of four students of 7th grades of the Junior High School in Probolinggo, each of them has a different learning style that is diverging, converging, assimilating, accommodating. Data collection is done by giving related statements about the property and concept of quadrilateral and asking them using semi-structured questioner to justify their statement. Data were analyzed based on mathematical justification indicators those are recognition, building-with, awareness. Recognition is the ability to recognize prior knowledge relevant to a mathematical situation. Building-With is the ability to apply prior knowledge for the purpose of the mathematical justification process. While awareness is the ability to show a clear summary to answer the truth of a statement.

Based on the results of research, the subject of diverging, converging, assimilating, and  accommodating showed differences those were not so far in the process of mathematical justification. They use prior knowledge (recognition) such as the definition, property, rule of the quadrilateral for the purpose of validating a statement in a quadrilateral material (building-with). However, students were only able to make a short descriptive summary so if it was read by someone then it was possible that they will understand why the reason must be solved by the way the calculation even though the answer is correct (awareness). This indicated that the students' justification ability was low because students were not accustomed to justifying their answers while the teacher still seldom explores students' justification ability.

The conclusion is generally the reasoning of the four subjects to the concept of a quadrilateral is still descriptive and concise, so their solution had not answered the 'why'. Their compact justification indicates that the ability of mathematical communication in writing is still low. In addition, two subjects who have diverging and accomodating  still have difficulty in distinguishing similar rectangular types which indicate that students' understanding was lacking.