The aim is to see whether the application of the Mastery learning approach can affect the ability to understand mathematical concepts. This type of research is quasi experimental design. The instrument used is a questionnaire. The hypothesis test used is a test statistic (t-test), but before that a normality and homogeneity test is done first. Data collection techniques needed are in the form of test questions understanding mathematical concepts. The results of the statistical test (t-test) that there is a good influence on the ability to understand the mathematical concepts of students with the application of the Mastery learning approach. Then it can be concluded that the ability to understand students' mathematical concepts is better with the Mastery learning approach than the ability to understand mathematical concepts with conventional approaches or lectures.