Discovery learning model with cognitive conflict approach is a teaching model that is designed with the aim to help students develop thinking skills by involving contradictory problems. The combination of the learning model with this approach means that the stages of the discovery learning model will be combined with the learning stages of the cognitive conflict approach. This study aims to determine the effectiveness of discovery model learning tools with cognitive conflict approaches to students' conceptual understanding. This research is part of developmental testing. The study design used one group pretest and posttest. The study population used 10th grade senior high school students in the city of Mataram and the sample used 65 students. The sampling technique used purposive sampling. The treatment used a discovery model learning tools with a cognitive conflict approach that has been validated previously. Data collection used the test method. The test instrument used was the conceptual understanding in multiple choice of 25 questions. Data collected were analyzed using descriptive statistical. The results showed that the use physics learning tools based on discovery model with cognitive conflict approach effective to improve students' conceptual understanding. The highest of conceptual understanding is on the subject  of the work. Discovery learning model with cognitive conflict approaches are also effective for increasing of conceptual understanding of every cognitive aspect.