This research aimed to know the effectiveness of learning materials based on guided discovery to increase students’ learning outcomes. The research model used in this study was Research and Development (R & D). Learning outcomes is gained through students’ learning outcomes assessment sheets. The results were analyzed by quantitative descriptive. The research design used one group pretest posttest design. The participants of the study were thirteen students. The results show that guided discovery learning materials was successfully increase a number of learning outcomes 32% on the middle category and 68% on the high category. Guided discovery learning materials has been developed according to the test results so that it can be used as an alternative way to increase students’ learning outcomes on thermochemistry materials.