The purpose of this study is to develop an instructional materials using discovery learning with cognitive conflict approach to improve vocational students understanding of heat concept. This instructional material was developed using the Four D model, namely define, design, develop, and disseminate. Furthermore, data were obtained from the syllabus, lesson plans, students' worksheet, learning material and conceptual understanding instruments in the form of multiple-choice question with the product categories validated by three experts. Data were collected by examining the achievement of the learning implementation and questionnaire responses of teachers and students that obtained very high practicality categories. Therefore, the instructional materials developed can be stated that feasible and practical to implement with a positive impact on students' conceptual understanding.