Motivation is very necessary for students in learning English. Student success in language mastery can increase along with increasing students' critical thinking skills. However, most high school students and above have a poor level of thinking in learning. Therefore, teachers must use appropriate learning models to improve students' critical thinking. The purpose of this research is to examine the impact of implementing the Flipped Classroom model on students' critical thinking skills. The samples are 38 high school students inĀ experimental class and 37 students in control class. The experimental class was taught using Flipped Classroom learning and the control class using conventional techniques. This research data is collected using a multiple-choice test from the Cornell Critical Thinking Test and a motivation questionnaire. Data analysis was carried out by testing hypotheses using t-test. The results showed that there were significant differences between critical thinking in the experimental class and the control class. So, the flipped class model in learning English is very suitable to use in learning.