Student?s Worksheet (SW) can help students to find a concept independently by solving every problem in it. To get SW that is suit to the needs, then in developing the SW it is needed to be combined with a learning model in accordance with student?s needs. One of learning models that can be utilized is Problem Based Learning (PBL). The PBL model is one of learning models that can train students\' critical thinking skills. The purpose of this research is to develop SW based on PBL to train students\' critical thinking skill. Research method of this paper is Research and Development which contains seven research steps: information collection, planning, initial product draft development, product testing (validation), product revision, field trial, and final products. Product validation includes content validity, construct validity, and legibility using questionnaires. Average score of content validity is categorized as excellent, construct validity as good, and legibility of the product as excellent category. So, it can be stated that SW is feasible to be used in the learning process. Moreover, teacher response result is categorized as excellent and students? response results good. The result of effectiveness test shows that post test score average is higher than pretest score average, and then experimental n-gain class score is higher than control class. Students\' critical thinking skills also improved in every indicator of critical thinking. Thus, it can be concluded that SW based on PBL as developed product of this research is effective in training students\' critical thinking skill.