In this study, it was aimed to test if seventh graders' thinking styles and mathematics self-concepts have significant difference according to mathematics achievement categories. The subjects participated in this study were 279 middle school seventh grade students from seven schools in Besiktas in Istanbul. In this study, descriptive research design was used. Students' mathematics self-concept was measured 'Self-Description Questionnaire-I' developed by Marsh (1992) and adapted into Turkish by Yildiz and Fer (2008). For the assessment of thinking styles 'Thinking Styles Inventory' developed by Sternberg and Wagner (1992) and adapted into Turkish by Fer (2005) was used. For the achievement in mathematics 'Mathematics Achievement Test' developed by the researcher was applied to the students. In terms of the study, the results demonstrated that according to mathematics achievement, categories the legistlative and executive thinking styles and mathematics self-concepts increased with higher mathematics achievement, but judicial thinking style didn't changed.