There is a growing body of research examining the impact of science field trips on pupils' learning in science education and the factors that influence their success. However, there is a limited number of studies that focus on the way teachers' beliefs influence their practices in an informal science-learning venue. This research aimed to investigate teachers' practices, when they plan, implement and comment upon the outcomes of a school visit to a science and technology museum in relation to their beliefs regarding the value of informal education, ways of supporting learning in an informal science-learning venue and the importance of familiarity with the venue. We studied 14 primary and secondary education teachers with respect to a visit they conducted with their class to a science and technology museum within a case-study approach. Interviews with the teachers, both prior to and after the school visits, and observations of the field trips were used to collect and verify our data. We applied a mixed analytical process, both inductive and deductive, to reveal different relations between teachers' beliefs and practices. Results show that there are close links between teachers' beliefs regarding the value of informal education and the learning processes within informal settings that influence their goals, roles and actions before, during and after the school visit. These results are discussed in light of teachers' need for in-service education regarding informal science education.