<p>This study investigates the impact of valence and valence ambiguity on silent word reading and memory recall using pupillometry. While emotional stimuli are found to influence pupil dilation, there have been mixed findings for the effects of valence in the literature. This study aimed to examine this effect by controlling for extraneous lexical variables (e.g., word and character frequency) and considering valence ambiguity as a distinct factor in linear mixed effects modelling analyses. Native Cantonese-speaking university students (<i>N</i> = 94) engaged in a silent reading task of 90 two-character Chinese words, with their pupillary responses being recorded, followed by a surprise memory recall test. The words varied in valence (negative, neutral, positive) and valence ambiguity (high, low). Analyses revealed that valence ambiguity increased pupil dilation, providing support for the deeper and more elaborated processing associated with words with higher valence ambiguity. While there was no significant effect of valence on pupil dilation, the valence × valence ambiguity interaction showed that negative words with higher ambiguity elicited greater pupil dilation than those with lower ambiguity. Memory recall performance was enhanced by valence ambiguity, independent of word valence, indicating that words with higher valence ambiguity foster more elaborated memory encoding even when it is incidental. These findings further our understanding of pupil dilation in emotional processing during silent word reading and the role of valence ambiguity during memory encoding.</p>