In this study, ambiguity was classified into cognitive and emotional ambiguity, and their effects on the aesthetic evaluation of haiku were examined for native Japanese and German speakers. Because haiku is the shortest form of poetry in the world, it usually contains ambiguity and makes cultural comparison easier. Overall, 450 Japanese and 373 German speakers participated in an online experiment involving the evaluation of haiku poetry. They were also asked to fill out questionnaires based on personality traits. Then, participants were asked to rate a haiku based on 10 characteristics, including the degree to which they perceived beauty, cognitive ambiguity, awe, and nostalgia. Results showed that as cognitive ambiguity increased, the aesthetic evaluation of haiku decreased. This tendency was greater among German than among Japanese speakers; this can be explained by the differences in high- and low-context societies. Regarding emotional ambiguity, this study focused on the higher-order emotions of awe and nostalgia, which encompass both positive and negative emotions. It was found that the greater the participants felt these emotions, the higher was their aesthetic evaluation of haiku. This tendency was greater among German than Japanese speakers; this may be because Westerners tend to perceive awe and nostalgia highly positively. Ambiguity, also known as “the beauty of silence,” is one of the characteristics of haiku and was found to be an important factor in aesthetic evaluation; however, this relationship was also influenced by cultural differences.