Psychological aspects must accompany critical thinking skills to solve math problems well, one of which is self-confidence. Self-confidence is one that students need because they can understand mathematics well, learn mathematics without giving up and show confidence in their mathematical abilities. This study analyzes grade VIII students' critical thinking skills at MTS Manbaul Ulum Gembong with flat-side building material in terms of students' self-confidence. This study used a descriptive method with a qualitative approach. The population in this study were all students of class VIII MTS Manbaul Ulum Gembong. The sample used was purposive sampling based on high, medium, and low self-confidence criteria for as many as 6 grade VIII students. The data collection technique used a critical thinking skill test instrument, self-confidence questionnaire, and interviews. Data analysis used triangulation techniques. This study's results indicate that in analyzing the mathematical material of flat-sided shapes with 1) students who have high self-confidence can solve interpretation, analysis, evaluation, and inference indicators. 2) students who have self-confidence can complete the analysis indicators, evaluation, and inference. 3) Students who have low self-confidence are only able to complete the analysis indicator.