This paper investigates mathematics teachers' beliefs regarding the roles of visualization for teaching fractions and algebra. The paper discusses the construct of beliefs and theoretical roles of visualization. We further give rationale for the qualitative approach of our study. In the results we compare two teachers' beliefs from a larger sample. We work out that, although both teachers use visual re pre sen tations in a similar way, they assign different roles to their respective use. Their beliefs appear to be stable across subdomains. We discuss our impression that the teachers emphasize other roles of visualization than educational research implies.