Epistemological beliefs refer to an individual's thinking and beliefs about the nature of knowledge and knowing. The present study examined two research questions: (1) how do prospective elementary teachers' epistemological beliefs in science change as a result of instruction specifically designed to improve their epistemological beliefs and (2) what role does the conceptual ecology for epistemological beliefs play in their development? The study was correlational with a sample of 161 prospective elementary teachers (148 female, 13 male). Self-report questionnaires tapping four dimensions of epistemological beliefs (certainty-simplicity, justification, source, attainability of truth) were given to prospective elementary teachers at two time points during an introductory science course. Results indicated that prospective elementary teachers became more sophisticated in their beliefs across all four dimensions of epistemological beliefs. It was found that one component of conceptual ecology for epistemological beliefs, thinking dispositions, was related to the development of epistemological beliefs. Prospective teachers with high thinking dispositions developed more sophisticated beliefs in comparison to prospective teachers with low thinking dispositions. (Contains 6 tables and 1 figure.)