Facial expressions in daily life typically change from one emotional state to another. To understand how people process emotions, it is important to know not only how current facial expressions are interpreted but also recent past expressions. While researchers have recently focused on perceptions of current expressions, little is known about how past expressions are gauged and about cultural differences in this process. The present research investigated whether and how evaluations of past facial expressions are influenced by subsequent expressions, and whether this process varies across East Asian and Western cultures. Specifically, Chinese and Canadian participants judged the degree of positivity/negativity of past expressions after viewing expressions that changed from past emotions-low-intensity smiles (Experiment 1), high-intensity smiles (Experiment 2), and anger (Experiment 3)-to current positive or negative emotions (collected between 2019 and 2020). All three experiments consistently found an assimilation effect, whereby past expressions were rated more positively when the current expression was positive than when the current expression was negative. Moreover, this assimilation effect was consistently greater in Chinese than in Canadian participants. Together, these findings suggest that the interpretation of past facial expressions assimilates toward the valence of subsequent expressions and that the impact of this temporal emotional context is more pronounced in Eastern relative to Western cultures. (PsycInfo Database Record (c) 2024 APA, all rights reserved).