The aim of this study is to investigate the effect of guided inquiry-based learning approach on students' academic achievement and science self-efficacy. In the study, a quasi-experimental model with pretestposttest control group was used. The research was carried out with 40 students studying in a public school located in the southeast of Turkey. Within the scope of the application, while the activities in accordance with the guided inquiry-based learning approach were carried out in the experimental group, the Science Curriculum (MoE, 2018) was applied in the control group. Strength and energy achievement test and science self-efficacy scale were used as data collection tools in the study. As a result of the research, it was concluded that guided inquiry-based learning approach had a significant effect on students' academic achievement and self-efficacy. In the study, various suggestions were made for researchers.