Penelitian ini bertujuan  mendeskripsikan keterlaksanaan model pembelajaran guided inquiry untuk meningkatkan keterampilan berpikir kritis peserta didik kelas X pada materi getaran harmonis, mendeskripsikan peningkatan keterampilan berpikir kritis peserta didik kelas X setelah diterapkan model pembelajaran guided inquiry, dan mendeskripsikan respon peserta didik terhadap penerapan model pembelajaran guided inquiry. Jenis penelitian yang digunakan adalah deskriptif kuantitatif dengan metode penelitian pre-experimental dan desain penelitian menggunakan One group pretest-posttest design, subjek pada penelitian ini berjumlah 102 peserta didik kelas X IPA di SMA Negeri 1 Ngimbang. Instrumen penelitian yang digunakan berupa lembar pengamatan keterlaksanaan pembelajaran, lembar tes berpikir kritis (pre-test dan post-test), dan angket respon peserta didik. Data yang terkumpul dianalisis dengan menggunakan analisis lembar keterlaksanaan, uji t berpasangan, perhitungan n-gain, uji ANAVA, uji Tukey, dan analisis lembar angket respon. Penelitian ini mendapatkan hasil bahwa (i) keterlaksanaan model pembelajaran guided inquiry pada materi getaran harmonis terlaksana dengan sangat baik dengan rata-rata persentase 88%, (ii) model pembelajaran guided inquiry pada materi getaran harmonis dapat meningkatkan keterampilan berpikir kritis peserta didik di ketiga kelas secara signifikan pada taraf signifikansi 5% dengan nilai rata-rata n-gain ketiga kelas sebesar 0,65 berkategori sedang. Berdasarkan uji ANAVA diperoleh bahwa terdapat perbedaan rata-rata n-gain, dimana perbedaan tersebut dapat diketahui dengan menggunakan uji tukey dan dihasilkan bahwa terdapat perbedaan rata-rata n-gain yang signifikan pada kelas X IPA 3 dan X IPA 5 (iii) Respon peserta didik terhadap pembelajaran fisika dengan model pembelajaran guided inquiry memperoleh rata-rata persentase 82% dengan kategori sangat baik.

This research aims to describe the implementation of guided inquiry learning to improve critical thinking skills of tenth grade students in harmonic motion topics, to describe improvement of critical thinking skills tenth grade students after applied guided inquiry learning model, and describe student’s response to the implementation of guided inquiry learning model. The type of research used quantitative descriptive with pre-experimental methods and one group pre-test and post-test design, subject in this research amounted 102 tenth grade science students in SMA Negeri 1 Ngimbang. Instrument used in this research was observation sheet of learning implementation, critical thinking test sheet (pre-test and post-test), and student’s response questionnaire. The data obtained were analyzed by analysis of the implementation sheet, paired T test, n-gain count, ANOVA test, Tukey test, and response questionnaire analysis. From this research, it if found that (i) the implementation of the guided inquiry learning model on harmonic motion topics is done very well with an average percentage of 88% (ii) guided inquiry learning model on harmonic motion topics can significantly improve student’s critical thinking skills in the three classes at significance level 5% with an average value of n-gain for all three classes is 0,65 in the medium category. Based on ANOVA test it was found that there were differences in the average n-gain , where the differences can be known by using the Tukey test and it was found that there were significant differences in the n-gain on the class X Science 3 and X Science 5 (iii). The response of students to physics learning with the guided inquiry learning model obtained an average percentage of 82% with a very good category.