Abstract: In Mathematics learning, justification is an important component forbuilding students' skills on mathematical reasoning, understanding concepts andmathematical communication. But in fact the students 'justification is still weakbecause teacher still rarely explores students' justification ability. This research isincluded in qualitative descriptive research because it aims to obtain a naturalpicture of the student's mathematical justification on the quadrilateral materialbased on Kolb's learning style. The subject of this study consists of four studentswho each have a different learning style that is diverging, converging,assimilating, accomodating. Data collection is done by giving related statementsabout the property and concept of quadrilateral and asking the subject to justifythe statement. Data were analyzed based on mathematical justification indicatorthat is recognition, building-with, awareness. Based on the results of research, thesubject of diverging, converging, assimilating, accomodating show differences inthe process of mathematical justification. In general the reasoning of the foursubjects to the concept of quadrilateral is still descriptive and concise, so it has notanswered the 'why'. Compact justification indicates that the ability ofmathematical communication in writing is still low. In addition, some subjectsstill have difficulty in distinguishing similar rectangular types that indicatestudents' understanding is lacking.

Keywords: Mathematical Justification, Kolb Learning Style