This research is aimed to produce a feasible guided inquiry instructional at designing a valid, practical, and effective teaching material through the employment of computer simulation on Junior High School solar system topic for improving students’ science process skill. This study was conducted by applying three stages from 4-D model, i.e. definition, design, development and was tried out in 7.1 class of SMP Negeri 5 Lubuk Alung, Padang Pariaman in the even semester of 2016/2017 academic year. The research design which applied in this study was One Group Pretest-Posttest Design. The measured research parameters were the validity, the practicality, and the effectiveness of the instructional tools. Observation method, questionnaire, and test were applied in data collection procedure. Data analysis technique applied quantitative and qualitative descriptive analysis method. The research reveals that the guided inquiry instructional tools through the employment of computer simulation on Junior High School solar system topic which was developed is valid, practical, and effective in developing students’ science process skill.