Interest in learning is an important aspect in the success of mathematics learning, especially at the elementary school level. This study aims to analyze the influence of the Realistic Mathematics Education (RME) model based on Batak Toba ethnomathematics on the learning interest of elementary school students in Mathematics subjects. The method used is a mixed method with a quasi- experimental design and a qualitative descriptive approach. The research sample consisted of two classes, namely the experimental class that received treatment using an ethnomathematics-based RME model and the control class that used conventional methods. This data collection technique was carried out through learning interest questionnaires, participatory observations, and in-depth interviews. Based on the analysis, the average value of the learning interest score in the experimental class increased from 58.75 to 78.40, while the control class only increased from 57.90 to 63.30. Independent T-tests showed significant results with sig values. (2-tailed) 0.000 < 0.05, which means there is a significant difference between the two classes. In addition, the results of observations showed the active involvement of students in contextual learning related to the Toba Batak culture, such as ulos patterns and number concepts in regional languages. Interviews with students and teachers also showed a positive response to culture-based learning. Based on the results of this study, it is concluded that the RME learning model based on Batak Toba ethnomathematics can significantly increase the interest in learning mathematics of elementary school students compared to conventional methods.