Critical thinking is very important for everyone because it is possible to evaluate opinions and be able to solve problems by keeping the reasons and steps to solve them. This study aims to produce learning tools in guided inquiry model to improve critical thinking skills. This type of research is development research using 4-D model design with the trial using one group pretest-posttest design. The instrument used is the observation sheet of learning implementation and the critical thinking skill sheet. Data analysis using quantitative descriptive. The results showed that the validity of the learning devices used categorized as valid, the learning was done entirely in a very good category and there was an improvement of students' critical thinking skills. Improvement of students' critical thinking skill test result resulted from learning in guided inquiry model having correlation with critical thinking indicator that was formulated problem, formulating hypothesis, analyzing, giving argumentation and determining an action, so that can be used as one of alternative in improving process Learning and improving the results of critical thinking skills. Based on the results of data analysis can be concluded that the instructional device inquiry guided inquired fit to be used to improve critical thinking skills.