The science curriculum aims to provide students with the identity of a researcher, thinking skills, and scientific process skills. Critical thinking skill emerges as one of the skills that should be emphasized in the teaching process in terms of its structural features and the qualities aimed to be given to individuals. For individuals to gain critical thinking skills, they must first gain critical thinking standards. The main purpose of this research is to examine the activities in the "Solar System and Eclipses" unit in the sixth-grade science textbook in terms of critical thinking standards. The qualitative research model was used in the research. The data source of the research is the sixth-grade science textbook used in the province of Isparta. The data of the research were collected using the document analysis method. In the analysis of the data, the analysis was made by applying the descriptive analysis method, one of the qualitative data analyses. In line with the analysis, in terms of critical thinking standards, the secondary school sixth-grade science textbook has been determined to meet the standards of clarity, accuracy, significance/relevance, sufficiency, breadth/depth, and precision at a high rate. Based on the research results, suggestions have been developed that textbooks from different disciplines should be examined in line with critical thinking standards and that the activities of different grade-level units in the science curriculum should be examined in terms of critical thinking standards.