Background <p>The main goal of this study was to examine the relation between inner (equanimity), and outer (postural stability) balance. It was expected that participants with a higher sense of equanimity, higher emotion regulation abilities, and higher executive control performance abilities would show better postural stability in an emotionally demanding situation. This hypothesis adds to the importance of emotion regulation in the assumed relation between equanimity and postural stability.</p> Methods <p>One hundred forty-seven young, healthy participants completed a postural sway task under emotionally demanding and neutral conditions. Emotion regulation strategies were measured using the affective style questionnaire, and attentional abilities were assessed using the attention network task.</p> Results <p>Participants with low equanimity had a higher sample entropy (higher complexity of postural stability signal) when emotion acceptance was low compared to high emotion acceptance. In participants with high equanimity, the effect reverses. However, the results were only obtained with one postural stability parameter, namely the parameter of sample entropy.</p> Conclusions <p>Inner and outer balance are somehow related, and the emotional regulation strategy of acceptance might play an important role. However, the results depend on measuring outer balance, and further studies must investigate the relationship in more depth.</p> Trial registration is not applicable <p><b>Preregistration</b>: This study was preregistered at OSF: <a href="https://doi.org/10.17605/OSF.IO/USPWF">https://doi.org/10.17605/OSF.IO/USPWF</a>.</p>