The assessment of self-regulation, which is important for the geometry learning area and can be associated with the stages of the ACE cycle, is important for success. The study was conducted to determine the effect of the ACE cycle-based learning process on students’ geometry self-efficacy beliefs in the 7th grade polygons learning area. Quasi-experimental design with pretest-posttest control group, one of the quantitative research methods, was preferred in the study. The study group consisted of a total of 46 students, 24 in the control group and 22 in the experimental group, studying in the seventh grade of a middle school in the eastern Anatolia region of Turkey. In the 4-week implementation, the lessons were conducted according to the ACE learning cycle in the experimental group, while no intervention was made in the control group. In this study, the Self-Efficacy Scale for Geometry was used as a data collection tool and independent sample t-test and dependent sample t-test were used to analyze the data. The results showed that the instruction shaped according to the ACE learning cycle was more effective on students' geometry self-efficacy beliefs in the related learning domain.