This research aims to improve the learning process and increase the student's mathematics learning outcomes through the implementation of Think-Talk-Write strategy in Cooperative Learning. This type of research is the Classroom Action Research with two cycle. The research was conducted in class VII1SMP Negeri 1 Kubu in the second semester of the 2016/2017 academic year with the subject of as many as 38 students. The research instrument consists of learning devices and instrument data collectors. Learning device used in this research is the Syllabus, Lesson Plan and Worksheet. The instrument data collector used in this research is the observation sheet and math achievement test Based on the result of the research showed that implementation of learning process on cycle II had happened improvement from implementation on cycle I. Weakness on cycle I is improved on implementation cycle II according with planning of improvement after reflection cycle I. Number of students that reach Minimum Mastery Criteria increase from basic score to daily test II. The number of students who reach Minimum Mastery Criteria on basic scor, daily test I and daily test II are respectively 13 person (34,2%), 17 person (44,7%) and 30 person (78,9%). Results of this research indicates that the implementation of Think-Talk-Write strategy in Cooperative Learningcan improve learning process and increase mathematics learning outcomes from the students at class VII1SMP Negeri 1 Kubuin the second semester academic years 2016/2017.