Misconceptions are errors in a concept that must be identified early, it is very important so that it does not become the cause of errors in the next concept. This study aims to analyze the causes of misconceptions of class X students at SMK Negeri 2 Banjarmasin on acid-base material which was measured using a four-tier diagnostic test instrument. This research method is descriptive quantitative-qualitative. Collecting data using test techniques with four-tier diagnostic test instruments and non-tests through interviews. The results showed that 41.46% of students experienced misconceptions of acid-base theory sub-concepts by 46.73% (medium category), the nature of acid-base solutions had misconceptions of 29.44% (low category), acid-base indicators had misconceptions of 41, 43% (medium category), acid strength (pH) 44.86% (medium category) and the calculation of the pH of the solution concentration of 44.86% (medium category). The causes of misconceptions of wrong intuition, associative thinking, students' abilities and students' learning interests