Berpikir kritis merupakan salah satu aspek penting bagi siswa selama proses pembelajaran. Realita yang ada pada siswa kelas VI SD di Sekolah Kristen Kalam Kudus Yogyakarta di umpan balik mentor, jurnal refleksi dan lembar kerja siswa menunjukkan kurangnya kemampuan berpikir kritis siswa pada pembelajaran IPA. Model pembelajaran kooperatif tipe group investigation dipakai untuk mengatasi masalah yang ada. Model Penelitian Tindakan Kelas yang digunakan berdasarkan model Pelton dilakukan sebanyak dua kali penerapan. Penelitian ini dilakukan di kelas VI SD Sekolah Kristen Kalam Kudus Yogyakarta yang berjumlah 17 siswa sejak 01 Agustus 2018 sampai 10 Oktober 2018. Sumber data yang yang digunakan yaitu lembar observasi mentor dan siswa, lembar kerja siswa, umpan balik mentor, jurnal refleksi, dan RPP. Tujuan dari penelitian ini yaitu untuk mengetahui apakah model pembelajaran kooperatif tipe group investigation dapat meningkatkan kemampuan berpikir kritis siswa kelas VI di Sekolah Kristen Kalam Kudus Yogyakarta dalam pembelajaran IPA. Hasil penelitian menunjukkan bahwa penerapan model pembelajaran kooperatif tipe group investigation dapat meningkatkan kemampuan berpikir kritis siswa. Dapat dilihat melalui lembar kerja siswa, dimana indikator pertama mengalami peningkatan 3 poin, indikator kedua 23 poin, indikator ketiga 27 poin, dan indikator keempat 13 poin. Peningkatan yang ada dikarenakan penerapan model pembelajaran kooperatif tipe group investigation dilakukan dengan amat baik dan adanya modifikasi yang disesuaikan dengan situasi dan kondisi kelas. /Critical thinking is one of the important aspects for students in their learning process. The reality of the sixth grade elementary school students at the Kalam Kudus Yogyakarta Christian School based in the mentor feedback, reflection journals, and student worksheets showed a lack of critical thinking skills in students in science learning. Cooperative learning model investigation group type is used to overcome existing problems. The Class Action Research Model used based on the Pelton model is carried out twice. This research was conducted in class VI of SD Kalam Kudus Yogyakarta Christian School, amounting to 17 students from 1 August 2018 to 10 October 2018. The data sources used were mentor and student observation sheets, student worksheets, mentor feedback, reflection journals, and lesson plans. The purpose of this study is to find out whether group investigation type of cooperative learning model can improve the critical thinking skills of class VI students at the Kalam Kudus Yogyakarta Christian School in the science subject. The results showed that the application of a group investigation type of cooperative learning model type can improve students' critical thinking skills. Can be seen through student worksheets, where the first indicator has an increase of 3 points, the second indicator is 23 points, the third indicator is 27 points, and the fourth indicator is 13 points. The increase is due to the application of the group investigation type of cooperative learning model that is carried out very well and some modifications are adjusted to the situation and condition of the class.