Mathematical reasoning ability is the ability to think logically to get a conclusion. This study aims to analyzing the effectiveness of Process Oriented Guided Inquiry Learning (POGIL) with Peer Feedback towards the students' achievement of mathematical reasoning abilities. The population in this study were 7th-grade students in one junior high school in Semarang in the academic year 2018/2019. This research is quantitative research. Sampling is done using random sampling techniques. The results showed that (1) the average mathematical reasoning ability of students in POGIL with Peer Feedback was more than or equal to the minimum specified completeness criteria, namely 65, (2) the proportion of students who reached 65 in POGIL with Peer Feedback more than or equal to 75%, (3) the average mathematical reasoning ability of students in POGIL with Peer Feedback is more than the average mathematical reasoning ability of students in Discovery Learning, and (4) the proportion of students who achieve grades 65 in POGIL with Peer Feedback is more than the proportion of students who reach 65 in Discovery Learning, (5) self-regulated learning of mathematics affects 30% of students' mathematical reasoning abilities.