The relations between self-efficacy and mathematics achievement were examined in this study. The research was carried out with 350 (51% male and 49% female) 7th grade students who are in different schools in the centre of Konya. Sources of mathematics self-efficacy scale was used to determine the self-efficacy sources of students and end-of-term mathematics grades were used to determine their mathematics achievement. Pearson Product-Moment Correlation Coefficient and Multiple Linear Regression Analysis were used in the analysis of the data. According to the results, there are high and medium-level significant relations between mathematics self-efficacy sources and mathematics achievement. The order of importance of self-efficacy sources on mathematics achievement is as follows: personal experiences, social persuasions, physiological states and vicarious experiences. Personal experiences, social persuasions and physiological states are significant predictors of mathematics achievement. Vicarious experiences have not a significant effect on mathematics achievement. The variables that predict the mathematics achievement explain nearly 59% of the change in mathematics achievement. Some recommendations were made for practice considering the findings.