Introduction: Odor stimuli can influence cognitive pro, including selective attention; however, it remains unclear whether these effects are driven by the chemical properties of odor compounds or by their semantic or emotional associations. The aim of this study was to clarify the mechanism by which olfactory inputs influence visual attention by isolating the effects of specific odor compounds from those of affective or semantic factors. Methods: To investigate this question, we assessed the effects of limonene, a key compound found in citrus odors, and lemon essential oil on visual attention, as indexed by the P300 component of event-related potentials, which reflect the allocation of selective attention. In the present experiment, participants completed a visual oddball task under three odor conditions: no odor, limonene, and lemon essential oil. Results: The findings indicated limonene presentation significantly reduced P300 peak amplitudes compared with that of the no-odor condition, whereas lemon essential oil had no such effect. Subjective ratings of pleasantness, congruency, and arousal did not differ significantly between the two odors. Conclusions: These results suggest that limonene modulates selective attention primarily through its chemical properties rather than through mood or semantic influences. This study provides new evidence for chemically specific olfactory–visual interactions and underscores the importance of distinguishing chemical effects from psychological mechanisms in cross-modal cognitive modulation.