This study aims to analyze students' errors in solving questions on relations and function material, based on the Kastolan stages. In this study, a qualitative descriptive method was used. This research was conducted on Class VIII students of SMPN 4 Cimahi with 29 participants. Data was collected through a written test consisting of 5 description questions, and any mistakes made by students were explained based on the Kastolan stages. To analyze the data, the researcher performed data reduction, data presentation and conclusion. The research results obtained that in the work of students found conceptual errors occurred because the students misunderstood the concept and did not know the formula to be used. Procedural errors occur because students do not write down or do not know the completion procedure, which indicates the student fails to continue the settlement procedure. Technical errors occur because participants do not understand the basic concepts properly, so students make calculation errors when solving problems. The conclusion from the results of this study is that it was found that students still experienced these three types of errors in solving the description questions on the material relations and functions
