<p>This study investigated how induced mood states and emotional facial expressions modulate susceptibility to the Ebbinghaus illusion. Participants received either a positive or negative mood induction before performing the illusion task, in which both the target and inducer circles were replaced by faces displaying angry, happy, or neutral expressions. Results showed that participants in the negative mood group demonstrated a stronger illusion effect when the Ebbinghaus illusion configuration included angry faces, whereas no significant differences across face valence were observed in the positive mood group. These findings suggest that negative mood selectively enhances perceptual integration in the presence of threat-related stimuli, amplifying contextual influences on size perception. In contrast, positive mood may promote cognitive flexibility, facilitating more stable perceptual judgments regardless of emotional context. This research highlights the interplay between internal mood states and external emotional cues in shaping visual perception, and extends our understanding of how emotions influence visual illusions.</p>