Social media users should have a critical approach and look at any of knowledge in social media environments through a rational lens outside of their personal beliefs. In the era of posttruth, the rational lens concerns the epistemological beliefs that are about questioning the source of knowledge and perceive knowledge with criticism. The purpose of this study was to develop the social media-specific epistemological beliefs scale. The dimensions for the scale to be developed in the study were determined on the basis of a theoretical structure earlier proposed in the literature. The development of the social media-specific epistemological beliefs scale consisted of five stages: creating item pool, content and face validity analysis, construct validity analysis, reliability analysis, and language validity analysis. The study group created to analyze the construct validity of the scale consists of 432 preservice teachers who are studying in the education faculty of a large state university in Turkey. As a result of exploratory and confirmatory factor analysis, the social media-specific epistemological beliefs scale was found to be composed of 15 items as a five-point Likert-type, which was fallen under three factors. Findings on the social media-specific epistemological beliefs scale showed that the scale was valid and reliable.