Difficulties in learning science especially in critical thinking skills are characterized by low mastery of concepts, misconceptions, and those related to contextual matters. Specifically developed learning set will be able to increase students' mastery of critical thinking skills. This research development aims to evaluate the validity, practicality, and effectiveness of the development of science learning set to develop critical thinking skills of junior high school students. The research subjects were 7th grade students of Muhammadiyah 3 MTs Al-Furqan Banjarmasin. The validity data of the learning set was obtained through the assessment of 3 experts. Data on the practicality of learning set include evaluating the implementation of lesson plans and students' responses to the small group test. Data about the effectiveness of learning set include: 1) the results of students' critical thinking skills; 2) cognitive assessment results. Data was collected through tests and observations and analyzed descriptively. The results showed that the science learning set developed were classified as valid based on the results of the validation, including the design of the learning set, format, material, language, presentation, supporting innovation and improving the quality of teaching and learning activities. Learning devices are also declared practical because they are easy to use by students. This is supported by: 1) The implementation of lesson plans in small group tests scores from the lowest 3.00 to the highest 4.00 in the practical to very practical categories; 2) Students give positive responses to the learning process. The effectiveness of science learning set has also been fulfilled, this is based on the findings of the study: 1) students' critical thinking skills in the field test are at least good categories; and 2) students' cognitive learning outcomes through field tests are in the good category (80 ≤ 100%).