Introduction: Early prediction and timely intervention are particularly essential for high-risk preterm infants. Brain magnetic resonance imaging (BMRI) is frequently used alongside functional evaluations to improve predictions of developmental outcomes. This study aimed to assess voxel-based brain volumetry in extremely preterm infants using BMRI at term equivalent age (TEA) and investigate its association with developmental outcomes. Methods: From March 2016 to December 2019, high-risk preterm infants (birth weight <1,500 g or gestational age <32 weeks) with BMRI at TEA and follow-up developmental data assessed by Bayley-III were included. For BMRI volumetry, manual tracing and segmentation were performed on T1-weighted scans, and after smoothing, voxels were calculated for each brain segment. Forty-seven subjects were enrolled and categorized into typical/delayed motor groups. Results: Results revealed a significant difference in ventricle size and ventricle ratio in BMRI at TEA between the groups. Even after controlling for other factors that could influence developmental outcomes, ventricle ratio emerged as a robust, single predictor for future motor development. Conclusion: This study suggests the potential clinical utility of BMRI volumetry in predicting motor development outcomes.