Critical thinking skills are one of the four skills needed in the 21st century. Critical thinking skills are so important that they need to be taught and included in the school curriculum. This research aims to: (1) describe the critical thinking skills of junior high school students in solving mathematical problems and (2) identify the students' critical thinking components in the analysis, evaluation, inference, explanation, and self-regulation sub-skills. This is descriptive research with a qualitative approach. Data was collected through a test and interviews, triangulation accomplished by comparing between test and interviews. This research involved 24 subjects comprising 9 male students and 15 female students. The test used in this research consisted of 6 problems representing 6 sub-skills of critical thinking skills. The results of data collection were analyzed through data reduction, data display, and conclusion drawing. The research results showed that: (1) the critical thinking skills of junior high school students were in a low category; and (2) the evaluation, analysis, and self-regulation sub-skills became the lowest critical thinking sub-skills mastered by the students compared to other critical thinking sub-skills.