This paper investigates how ambiguity attitudes affect people’s willingness to enter a gender incongruent field dominated by the opposite gender. In an online experiment, subjects performed both a male-typical and a female-typical task. They had to choose one of the two tasks to compete with other subjects and win a prize if they were among the top 50% performers. We elicited subjects’ ambiguity attitudes concerning their ranking in the two tasks. We found that 49% of men, as compared with 33% of women, chose to compete in the gender incongruent task. Both women and men were more ambiguity averse towards their ranking on the gender incongruent task. Controlling for actual performance, this extra ambiguity aversion made people less willing to compete in gender incongruent tasks. This suggests that ambiguity is an important factor contributing to the underrepresentation of one gender in professions populated by the opposite gender (e.g., women in STEM fields). Our findings open up an additional channel, ambiguity attitudes, where policymakers may tap in to reduce the ongoing gender inequality.