This study aims to determine the mathematical reasoning ability of class VIII students of SMP Negeri 6 Palembang on the material of building a flat side space with the PBL model. This type of research is a descriptive study with the research subject being 11 students of class VIII.6 SMP Negeri 6 Palembang. Data collection using a written test consists of 5 questions on the flat side of the bloc…