This research aimed to determine students' critical thinking skills by applying the guided inquiry learning model to the reaction rate material. This type of research is a pre-experimental design, with a One-Group Pretest-Posttest Design. This research was conducted on 36 students in class XI MIPA 6 SMA Negeri 1 Menganti Gresik who had not received material about reaction rates. The outcome of this study indicate that: (1) The application of the guided inquiry learning model at the first meeting got a percentage of 95%, at the second meeting 96% with a very good category; (2) Percentage of relevant activities is higher than irrelevant activities; (3) Students' critical thinking skills were successfully trained with an increase in the test as seen through the average N-gain value on the interpretation indicator of 0.86 (high), the inference indicator of 0.83 (high), the analysis indicator of 0.77 (high), and an explanation indicator of 0.80 (high); (4) Cognitive learning outcomes obtained by students showed an increase between pretest and posttest, with an average n-gain value of 0.84 in the high category and from the results of the paired sample t-test, Sig. (2-tailed) 0.000 < 0.005, so there is a significant difference; (5) Student responses to the applied learning model, namely guided inquiry, were very good with a percentage of 95%. This result indicates that the guided inquiry learning model can train the critical thinking skills of class XI students on the reaction rate material.