This study aimed to find out the activity and learning outcomes of the eight grade mathematics students at SMP N.2 Sipahutar in academic year 2017/2018 on the application of Bruner's theory on the subject of parallel lines. The subject of this research was the eight grade students of SMP N.2 Sipahutar in academic year 2017/2018, while the object of research was the result of learning and students' activity while learning with the application of Bruner's theory on the subject of parallel line. This research was a descriptive research, and the instrument of data collection used was the test in the form of description and students' activity observation sheet. Based on the result of data analysis, the results of the research are: (1) The average score of learning result obtained by students is 24.64 with the average grade 77.02 or with the percentage of mastery level of 77.02%. It shows that the students' level of mastery is still classified as moderate. (2) Student's learning completeness: a) Persuasion ability, many students who completed the study were 27 students, while the unfinished study was 4 students, b) Classical absorption, from 31 students there are 27 students or 93.55% completed the study, while the unfinished study is 4 students from 31 students or 6.45%. It shows that classically, the students' learning completeness is achieved; (3) Achievement of specific learning objectives was over 65.0%. (4) Students' activity, activity level on first learning is equal to 75,71 and the mean of students' activity reliability level is equal to 82,62%; students' activity level on the second learning is equal to 88,82 and the mean of students' activity reliability level is equal to 84,61%, it concluded that there is increase of students' activity during learning.