Improving math skills is considered important today. Because mathematical abilities can encourage individuals to be able to solve problems in the midst of society. A number of studies have proven that self-concept is very influential on mathematical ability. Therefore, this study wants to prove again whether self-concept and interest have an effect on mathematical ability. In order to prove this question, this study uses a quantitative type of research with an ex-post facto research approach. The sample in this study amounted to 24 students (male = 3 and female = 21). The instrument used in this study is the self-concept and interest scale adapted from Sproesser et al (2016) and individual mathematical abilities were taken from the Grade Point Average. This study uses linear regression analysis techniques. The results showed that self-concept is very influential on the mathematical ability by 0.04 (p<0.05). That is, to improve the individual's mathematical ability must have self-concept maturity and interest in mathematics.Keywords: self-concept, mathematical ability, ex-post facto research