The increasingly complex development era provides demands to the world of education in order to produce competent Human Resources in various competencies, especially the potential for critical thinking. The 21st century education process is not just an educational process to make children know and understand a certain amount of knowledge. 21st century learning includes critical thinking skills, creative thinking skills, communication and collaboration. Critical thinking skills are high level thinking skills logically and critically using deep reasoning to consider emerging ideas. The method used in this research is descriptive research method. The level of mastery of students' critical thinking skills is obtained by dividing the scores obtained by students with a maximum score multiplied by one hundred percent. Based on the results of data analysis and discussion it can be concluded that the critical thinking skills of SMPN 1 Piani students are still relatively low.