Interoception, the internal perception of bodily states such as heartbeat and hunger, plays a crucial role in shaping cognitive and emotional states. Given that postural control affects cognitive and emotional processing, exploring postural effects on interoception could help uncover the neural mechanisms underlying its effects on cognition and emotion. In this study, we aimed to investigate how different postures affect interoception by using heartbeat-evoked potentials (HEPs), which are event-related potentials indicative of heartbeat processing in the cortex. The study included 21 healthy male participants. They were asked to sit in a chair (sitting condition) and stand (standing condition) in a relaxed state. Data from 64-channel electroencephalogram (EEG) and electrocardiogram (ECG) were collected. The EEG data were segmented by the R-wave timing detected from the ECG data for HEP analysis. HEPs were calculated by focusing on the 350–500 ms post-R-wave interval in the central and temporal brain regions. A paired t-test was performed to compare HEP amplitudes between the sitting and standing conditions, revealing significantly lower HEP amplitudes in the standing condition than those in the sitting condition (t=2.63, p=0.016, d=0.59). Furthermore, we explored the relationship between HEP changes and physiological changes such as cardiac activity and spontaneous EEG, finding no significant correlations (p>0.05, |r|<0.26). These findings suggest that the decreased HEP amplitudes observed during standing reflect attenuated interoceptive processing probably due to a redistribution of attentional resources from internal to external sensory processing, necessary for maintaining standing posture. Thus, postural differences may influence specific neurophysiological processes linked to interoception.