This study aims to describe the effect of realistic and scientific approach on student's learning achievement, mathematical reasoning ability, and interest. This study is a quasi-experimental study using the pretest-posttest nonequivalent group design. The research sample was randomly selected from six classes, three classes were elected. The instrument used in this study is the learning achievement test, a test of mathematical reasoning ability, and an interest-in-learning questionnaire. To test the effectiveness of teaching realistic and scientific mathematics approach, as well as conventional teaching using one sample t-test. The research findings indicate that the teaching realistic mathematics approach is effective on student's learning achievement, mathematical reasoning ability, and interest; the teaching scientific approaches is effective on student's learning achievement, and interest, but is not effective in mathematical reasoning ability; whereas conventional teaching is not effective on students learning achievement, mathematical reasoning ability, and interest. The teaching realistic and scientific mathematics approach has an effect and is more effective than conventional teaching on student's learning achievement, mathematical reasoning ability, and interest. The realistic mathematics approach is more effective than a scientific approach on student's learning achievement, mathematical reasoning ability, and interest
