This study aimed to develop conceptual-conflict-based learning device in mathematical problem solving on the subject of equations in three variables systems in the class X at MIA MAN 1 Makassar which was valid, practical and effective. The type of this study was research and development which consisted of: Lesson Plans, Student Book, Student Worksheet, and Learning Outcomes Test. The developmental model used was 4D model which consisted of difining, designing, developing and disseminating. The result of this study obtained that learning device was valid criteria based on the assessment from two validators. While the result of the limited trial showed the learning device was practical, but there were still several suggestions from observers that need to be considered to improve the practicality of the device. It was also effective which was proved by the completeness of learning outcomes that has been achieved, students’ activity was as expected, the ability of teachers to manage the learning was in a high category and the students’ responses was in a positive category.