The Group Discussion Method is a way of presenting a lesson in that students are faced with a problem - a problematic statement to be discussed and solved together. The distinctive feature of this learning method is that learning that takes place is carried out in the form of study groups. The objectives of this study are: 1) to describe the learning process by applying the Group Discussion Method to the subject matter of the animal life cycle in Mathematics in class V SDN 078489 Orahua. 2) to describe the increase in student learning outcomes by applying the Group Discussion Method to Mathematics in SDN 078489 Orahua. This research was conducted at SDN 078489 Orahua with the research subjects of the fifth grade students of the 2018/2019 academic year, total 27 students. The research method used is classroom action research (CAR). The research instrument used was (1) observation sheets for students who were not active in the learning process (2) observation sheets for students who were active in the learning process (3) observation sheets in the learning process of teacher respondents. (4) Test of learning outcomes, (5) Photo documentation. Based on the data analysis, it was found that: (1) The learning process by applying the Group Discussion Method in class V SDN 078489 Orahua in Mathematics subject was improved where the average result of reflection at the end of the cycle reached 84% (2) Student learning outcomes improved with the application of the Group Discussion Method in class V SDN 078489 Orahua in Mathematics subject, where at the end of the cycle the average student learning outcomes reached 80 with a percentage of 81% completeness.