The purposes of the study were to assess preservice teachers' domain-specific epistemological beliefs and to investigate whether preservice teachers distinguish disciplinary differences (physics, chemistry, and biology) in domain-specific epistemological beliefs. Mixed-method research design guided the present research. The researcher explored three epistemological dimensions: certainty and simplicity of knowledge, justification for knowing, and source of knowledge. Both quantitative and qualitative results suggested that a domain-specific epistemological beliefs system is a valid model to describe preservice teachers' epistemological beliefs. In terms of epistemological beliefs, disciplinary differences in physics, chemistry, and biology were discussed in the last parts of the study.