Berdasarkan pengamatan yang dilakukan di kelas VIII A di SMP Kristen ABC Manado, peneliti menemukan bahwa kemampuan berpikir kritis siswa masih kurang dan metode ceramah yang diterapkan kurang memfasilitasi siswa untuk berpikir kritis. Peneliti memutuskan untuk menerapkan metode eksperimen sebagai solusi untuk kendala yang terdapat di kelas VIII A. Penelitian ini bertujuan untuk meningkatkan kemampuan berpikir kritis melalui penerapan metode eksperimen, serta mengetahui bagaimana menerapkan metode eksperimen dalam meningkatkan kemampuan berpikir kritis siswa. Metodologi penelitian yang digunakan oleh peneliti adalah penelitian tindakan kelas (PTK) model Kemmis dan Mc Taggart yang berlangsung selama tiga siklus. Penelitian dilakukan pada tanggal 11 September – 13 November 2015 pada 25 siswa. Metode pengumpulan data yang digunakan peneliti adalah lembar angket siswa, lembar wawancara mentor, lembar observasi mentor, LKS (Lembar Kerja Siswa), jurnal refleksi, dan rubrik. Berdasarkan data yang didapatkan terbukti bahwa metode eksperimen dapat meningkatkan kemampuan berpikir kritis siswa. Terbukti bahwa siswa mampu mencapai tiga indikator kemampuan berpikir kritis yang sudah ditentukan peneliti dengan presentase 75% dari jumlah siswa keseluruhan mampu mencapai ketiga indikator tersebut. Kemampuan berpikir kritis siswa mengalami peningkatan dengan menerapkan metode eksperimen. Pada penerapannya, siswa diinstruksikan untuk membuat rumusan masalah, melakukan percobaan, mengamati hasil percobaan, menuliskan data pengamatan, dan membuat kesimpulan dari kegiatan eksperimen. Maka dapat disimpulkan bahwa penerapan metode eksperimen adalah upaya yang tepat dalam meningkatkan kemampuan berpikir kritis siswa. / Based on the observation toward grade VIII A students in a Christian Junior High School in Manado, the researcher found that the students’ critical thinking were still lacking and the lecture method that was applied less to facilitate students to think critically. Researcher decided to apply the experimental method as a solution to the constraints contained in the class VIII A. This research aimed to increase crirical thinking skills through the implementation of the experimental method, as well as knowing how to apply the experimental method in order to increase students’ critical thinking skills. The research methodology used was Classroom Action Research (CAR), adapting the Kemmis and McTaggart model and it lasted for three cycles. The research began from September 11th until November 13th, 2015, with 25 students as the research subject. Data collection methods used by researcher were student questionnaire sheet, mentor interview sheet, mentor observation sheet, student worksheet, reflective journal, and rubric. Based on the data obtained, the implementation of experimental method could increase students’ critical thnking skills. It was proved that students were able to achieve the three indicators of critical thinking that had been determined by the researcher, which was 75% of the overall student is able to achieve three indicators. Critical thinking skills of students had increased by applying the experimental method. In practice, the students were instructed to make the formulation of the problem, doing experiment, observing the result of the experiment, write observational data, and make conclusions from experimental activities. It could be concluded that the implementation of the experimental method is appropriate effort to increase students’ critical thinking skills.