Extensive theoretical research highlights the significant role of ambiguity attitudes in shaping household financial decisions, yet empirical studies in this area remain scarce. This research, conducted in collaboration with a leading insurance technology platform in China, involved a survey to measure individual ambiguity attitudes and track their critical illness insurance purchasing decisions. The empirical findings are as follows: Firstly, there is a positive correlation between an individuals aversion to ambiguity and the likelihood of purchasing critical illness insurance. On average, a one standard deviation increase in ambiguity aversion is associated with a 0. 61 percentage point rise in the probability of buying the insurance. This result holds robust even after controlling for risk attitudes and other demographic characteristics. Secondly, this study explored the heterogeneous impact of individual trust level, finding that among individuals lacking trust, the positive relationship between ambiguity aversion and the probability of purchasing critical illness insurance is weakened. Thirdly, the impact of ambiguity attitude on critical illness insurance purchase decisions is more significant among groups with lower income and higher educational levels. This study is the first empirical test of the relationship between ambiguity attitudes and critical illness insurance purchasing decisions. It also provides insights into understanding the influence of ambiguity attitudes on household financial decisions and promoting the healthy development of the commercial health insurance market.