Background <p>Postural instability linked to fear of movement (FOM) is a frequent impairment among adults with chronic low back pain (LBP). However, progressive stability thresholds on sway control remain poorly characterized.</p> Purpose <p>This study aimed to examine differences in sway excursion boundaries and circular stability thresholds during unilateral standing on the dominant and non-dominant limbs in adults with LBP.</p> Methods <p>Eighty adults (35 with LBP and 45 controls) participated in this study. Participants completed the Tampa Scale for Kinesiophobia (TSK) to assess fall-related fear. They performed three unilateral standing trials per limb on a force platform. Sway excursion boundaries were evaluated at 25%, 50%, and 75% circular thresholds within a 10&#xa0;cm radius.</p> Results <p>During dominant limb standing, there was a group interaction on trial and threshold (F = 6.80, <i>p</i> = 0.01). The LBP group showed greater sway excursions than the control group at 25% and 50% thresholds in the second trial and at 25%, 50%, and 75% thresholds in the third trial. During non-dominant limb standing, however, there was no group interaction on trial and threshold (F = 0.35, <i>p</i> = 0.56). There was no significant TSK interaction, regardless of limb dominance.</p> Conclusion <p>Adults with chronic LBP exhibit progressive postural instability under increasing balance demands, particularly during dominant limb standing. Although individuals with LBP demonstrated elevated FOM, it did not significantly influence postural sway outcomes. These findings underscore the importance of developing targeted, task-specific balance interventions to enhance dominant-limb stability in adults with chronic LBP.</p>