This study aims to describe the student worksheets feasibility theoretically. The type of this research is a development research which refers to 4-D model. However, this research was conducted for the first three stages. The data gained are analysed descriptively. The theoretical feasibility of the student worksheets was determined based on the result of validation. The results show that the student worksheet 1 and student worksheet 2 developed are theoretically feasible based on the criteria of content, presentation and language. In details, the criteria of content, presentation and language of student worksheet 1 get the average scores of 3,58; 3,75; and 3,83. The criteria of content, presentation and language of student worksheet 2 obtain an average score of 3,69; 3,58; and 4. Based on these results, it can be concluded that the student worksheets are feasible theoretically. Keywords: student worksheet, critical thinking, theoretical feasibilities.