This research aimed to describe the critical thinking ability of students’
mathematics in SMP Negeri 1 Baturraden viewed by self-concept. The research
was done in seventh H class on Mei 2018. The method that was used in the
research was qualitative method. The sampling used purposive sampling
technique. The subject of the research consisted into three categorize they are,
high, low, and middle. The data collection used questionnaire, essay, interview,
and documentary. The result of the research showed: 1) some students in high
self-concept categorize could master five indications of critical thinking ability of
students’ mathematics namely, analyzing ability, synthesizing ability, problem
solving ability, concluding ability, evaluating ability; 2) some students in middle
self-concept categorize only mastered three of five indications of critical thinking
ability of students’ mathematics namely, analyzing ability,synthesizing ability, and
evaluating ability, then; 3) some students in low self-concept categorize could not
master five indications of critical thinking ability of students’’ mathematics
namely, analyzing ability, synthesizing ability, problem solving ability, concluding
ability, evaluating ability.