This study, in which the explanatory mixed design was used, has two aims. The first aim is the development of a scale to determine teachers' beliefs about the integration of mathematics and children's literature. The second one is to examine the beliefs of teachers on children's literature and mathematics teaching, with the data collected through the scale. The items of the scale developed within the scope of the study were created based on the literature and the opinions of 56 teachers who were aware of this topic (phase 1). The draft scale was applied to 392 teachers. After the validity and reliability studies, the scale was finalized. Accordingly, the scale has four dimensions and 33 items: positive pedagogical effects of the integration, the role of resources influencing the integration process, teacher competencies that make the integration process difficult and social norms, and teacher competencies that facilitate the integration process (phase 2). The data were collected from 772 pre-school, primary, and middle school teachers (phase 3) to reveal teachers' beliefs about the mathematics and children's literature integration through the final form of the scale. The results indicate that pre-school teachers have much higher scores in contrast to the primary and middle school teachers except for the dimension of the role of resources influencing the integration process, and novice teachers have more positive beliefs about the positive pedagogical effects of integration and their competencies in this regard. Also, the beliefs about the integration process significantly vary based on the awareness levels about integration.