In the process of learning mathematics, mental retardation student require certain methods, strategies, and teaching materials that can help in overcoming difficulties during the learning process, including in learning mathematics. The importance of learning that presents the real world or the nature around in learning is expected to help the student in achieving learning goals in mathematics. The absence of mathematical teaching materials that can bring the real world to the child's mental retardation into the learning of mathematics. Learning that can bring the real world into learning is realistic mathematics education (RME). It is hoped that the existence of teaching materials based on realistic mathematics can help the difficulties faced by students of mental retardation in the process of learning mathematics. The research that has been carried out at this stage resulted in the worth of materials that are suitable to be used from six validator. In developing this teaching materials using the stage of research and development is the stage of existing product analysis, design stage design, internal test stage (expert validation), test phase (limited test and field test). Development stage that has been done is internal test stage that is expert validation. From the results of the study can be concluded that RME-based mathematics teaching materials that have been developed the criteria worthy of use based on the validation of six validators. This teaching material obtained an average validation value of 80.25% in the Eligible category.