Education aims to prepare students to become independent generations who are able to face the challenges of the times by having 21st century life skills, one of which is critical thinking, in fact contrary to the low critical thinking skills that occur in SMAN 2 Probolinggo. The purpose of this study was to describe the application of guided inquiry learning in improving critical thinking skills. This type of research is Class Action Research (CAR). Data is analyzed by triangulation through the process of data reduction, data presentation, and conclusion drawing. Research Results guided inquiry learning model can change the way students learn to practice high-level thinking through learning syntax so that it gives the impact of increasing critical thinking skills by 18.75% students of class XI IPA 1 Probolinggo 2 High School.