Mathematics learning is one of learning that can train and develop thinking skills. Unfortunately, teacher has been found and concerned in teachinglearning process because of the low critical thinking skill and learning motivation shown by students. Therefore, teacher takes improvement action with Classroom Action Research (CAR) through the implementation of Think Pair Share (TPS). This study aims to: (1) describe the process of implementation TPS to improve students’ critical thinking skill, learning motivation, and learning achievements, (2) analyze the development of students’ critical thinking skill, (3) analyze the development of students’ learning motivation, (4) analyze the development of students’ learning achievements, (5) identify the obstacles during TPS implementation process and how to solve them. This study was conducted for 3 cycles in the 7th grade of Ichthus School, with 12 students as the subject. Data were collected by using observation, field notes, written tests, questionnaire, and analyzed with descriptive qualitative. The results showed that the learning process is based on the implementation of Think Pair Share was done according to the steps; the achievement of students’ critical thinking skill cycle 1 is 70,42%, cycle 2 is 81,92%, cycle 3 is 90,83%. The achievement of students’ learning motivation cycle 1 is 73,10%, cycle 2 is 82,42%, cycle 3 is 92,92%. The students’ learning achievements also show improvement, which can be seen cycle 1 is 66,25%, cycle 2 is 76,33%, cycle 3 is 90,66%. The problem faced during implementation were students who still not get used to in applying the steps of process skills, students who do not work actively in groups, and the limited amount of instructional time. / Pembelajaran matematika merupakan salah satu pembelajaran yang dapat melatih dan mengembangkan kemampuan berpikir. Tetapi guru mengalami kerisauan dalam mengajar di kelas karena rendahnya kemampuan berpikir kritis dan motivasi belajar siswa. Akibatnya, hasil belajar siswapun rendah. Oleh karena itu, guru melakukan tindakan perbaikan dengan Penelitian Tindakan Kelas (PTK) melalui penerapan Think Pair Share (TPS). Tujuan penelitian ini adalah: (1) mendeskripsikan proses penerapan TPS untuk meningkatkan kemampuan berpikir kritis, motivasi belajar, dan hasil belajar siswa, (2) menganalisis perkembangan kemampuan berpikir kritis siswa, (3) menganalisis perkembangan motivasi belajar siswa, (4) menganalisis perkembangan hasil belajar siswa, dan (5) mengidentifikasi kendala-kendala yang dihadapi selama proses penerapan TPS. Penelitian ini dilakukan dalam 3 Siklus di kelas VII SMP Ichthus Jakarta, dengan subjek penelitian 12 siswa. Data dikumpulkan melalui observasi, catatan lapangan, tes tertulis, angket serta dianalisis secara kualitatif deskriptif. Hasil penelitian menunjukkan bahwa tindakan perbaikan yang dilakukan sesuai dengan langkah-langkah Think Pair Share (TPS); kemampuan berpikir kritis Siklus 1 mencapai 70,42%, Siklus 2 mencapai 81,92%, Siklus 3 mencapai 90,83%. Perkembangan motivasi belajar siswa Siklus 1 mencapai 73,10%, Siklus 2 mencapai 82,42%, Siklus 3 mencapai 92,92%. Peningkatan hasil belajar siswa Siklus 1 mencapai 66,25%, Siklus 2 mencapai 76,33%, Siklus 3 mencapai 90,66%. Kendala-kendala yang dihadapi yaitu siswa yang masih belum terbiasa melakukan tahapan TPS dalam proses pembelajaran, siswa yang kurang aktif dalam kelompok, dan keterbatasan waktu pembelajaran.