Gender has become a focus of mathematics education research. While some research show that there are no differences between boys and girls, numerous research studies have indicated that boys have outperformed girls. It is suggested that gender stereotypes, such as expecting girls to show less achievement in mathematics compared to boys, have an effect on mathematics achievement. According to these gender stereotypes, boys are more successful in mathematics and science and girls are more successful in literature and arts. Gender stereotypes are transmitted by one generation to the next generation via children's books, language, parents and teachers as well. Because of teachers' important role of shaping their students' beliefs and attitudes, determining teachers' gender stereotypes is vital to understanding the differences of mathematical achievement between girls and boys. Therefore, the purpose of this study is to develop a teachers' gender stereotype scale toward mathematics. The scale consists of two subscales: the Boys' Form and the Girls' Form. These two forms are conducted with 595 primary school teachers. Results of the exploratory factor analysis for each form, 17 items and four factors are determined. Based on the literature review, these factors are named as environment, gender appropriateness of careers, competence and attribution of success. For each form, the confirmatory factor analysis is conducted and the four factors of the subscales are confirmed. The findings of the study revealed that the scale is a valid and reliable instrument to measure gender stereotypes in mathematics.