Background/purpose: This research aims to classify and show the characteristics of the types of abstract thinking students use when solving mathematical problems. Materials/methods: This descriptive qualitative research was conducted in a structured manner on students of the University of Muhammadiyah Surakarta, Faculty of Teacher Training and Education, Mathematics Education Study Program, semesters 3, 5, and 7. The instruments of this research include a two-variable linear equation (SELTV), story questions, and audio-visual recording tools. Data collection is carried out through tests. The data is analyzed through data reduction, presentation, and conclusion. Results: This research finds a way to solve problems directly from the subject's thinking. Its findings are in the form of three classifications of abstract thinking: reflective abstraction, connected abstraction, and visual abstraction. Conclusion: This research identifies and classifies the types of abstract thinking students use in solving mathematical problems, such as symbolic, logical, connective, and visual thinking. Every kind of abstract thinking plays an important role in solving various mathematical problems, including systems of linear equations in two variables.