Abstract: This research aims to descript validity of students’ book for practicing students’ critical thinking skills. The research used descriptive quantitative method. Instruments data collection used validation questionnaires. Data analytical techniques used quantitative descriptive data analysis. Research result shows that the validity of students’ book and related instruments are declared very valid. Based on the discussion of the results and findings, it was concluded that students’ book that have been developed in natural science subject are suitable to be used to practice students critical thinking skills.