This research aimed at knowing the effect of implementing peer instruction integrated guided inquiry model on reaction rate lesson toward student critical thinking ability.  it was conducted at the first semester in the academic year of 2018/2019, and it was on reaction rate lesson at the eleventh-grade students of natural science 1 and 2 of state senior high school 2 tapung, kampar regency.  it was a quasi-experiment with pretest-posttest group experimental design.  51 students were the samples, and purposive sampling technique was used in this research.  instruments were essay test in the form of pretest and posttest and observation sheet.  the obtained data showed that there was a significant effect of peer instruction integrated guided inquiry model on reaction rate lesson toward student critical thinking ability, about 8,4%. Keywords: guided inquiry, peer instruction, critical thinking ability, reaction rate.ABSTRAK. Penelitian ini bertujuan untuk mengetahui pengaruh penerapan model pembelajaran inkuiri terbimbing integrasi peer instruction pada materi laju reaksi terhadap kemampuan berpikir kritis siswa. Penelitian ini dilaksanakan pada 2 kelas yaitu XI MIA 1 dan XI MIA 2 SMA Negeri 2 Tapung Kabupaten Kampar tahun ajaran 2018/2019. Jenis penelitian ini adalah quasi eksperimen dengan design pretes-postes. Sampel sebanyak 51 orang siswa dengan teknik pengambilan sampel purposive sampling. Instrumen penelitian berupa tes essay dan lembar observasi. Data yang diperoleh menunjukkan bahwa terdapat pengaruh yang signifikan dari penerapan model pembelajaran inkuiri terbimbing integrasi peer instruction pada materi laju reaksi terhadap kemampuan berpikir kritis siswa sebesar 8,4%.Kata kunci: inquiri terbimbing, berpikir kritis, laju reaksi