Prior research on epistemic beliefs, that is, individuals' views about knowledge and knowing, has mainly focused either on individuals' professed beliefs (as reported in questionnaires) or on their enacted beliefs (as indicated during task processing). However, little is known about the relation between professed and enacted epistemic beliefs. The present study focused on beliefs about the uncertainty of scientific knowledge and investigated both professed and enacted beliefs in the context of evaluations of scientific controversies. Participants were N = 79 university students who first completed a questionnaire that targeted their professed uncertainty beliefs about scientific knowledge. Then, approximately 1 week later, they completed a standardized test in which they evaluated five scientific controversies. Cued retrospective verbal reports were used to measure their enacted uncertainty beliefs while taking the test. Results revealed that professed and enacted uncertainty beliefs were interrelated and that both variables predicted individuals' performance with regard to the evaluation of scientific controversies. Furthermore, the effect of professed uncertainty beliefs on controversy-evaluation performance was partly mediated by enacted uncertainty beliefs. The findings of the present study point toward novel theoretical insights and educational implications regarding the relations between professed and enacted beliefs about the uncertainty of scientific knowledge and their role in individuals' evaluation of scientific controversies.