Background <p>We aimed to evaluate longitudinal changes in ultrashort echo time (UTE) two-component biomarkers reflecting graft ligamentization after anterior cruciate ligament (ACL) reconstruction and to identify associated clinical factors.</p> Materials and methods <p>Patients who underwent ACL reconstruction were prospectively included to perform 3-T three-dimensional double-echo UTE sequence at 3, 6, and 12 months postoperatively. Mean values of short T2* (T2*_s), long T2* (T2*_l), and fast fraction (FF), <i>i.e</i>., the signal proportion attributed to the T2*_s component, were calculated by fitting a biexponential model. Changes were analyzed using repeated measures analysis of variance−ANOVA. Multiple linear regression was used to assess associations between clinical factors and UTE parameters at 12 months.</p> Results <p>Forty-two patients (20 males), aged 32.7 ± 15.0 years (mean ± standard deviation), were enrolled. T2*_s and T2*_l increased from 3 to 6 months (T2*_s, 5.3 to 5.7 ms; <i>p</i> = 0.017; T2*_l, 21.1 to 23.3 ms; <i>p</i> &lt; 0.001), then decreased from 6 to 12 months (T2*_s, 5.7 to 5.0 ms; T2*_l, 23.3 to 21.1 ms; both <i>p</i> &lt; 0.001). FF followed the opposite trend, decreasing from 0.29 to 0.25, then increasing to 0.30 (both <i>p</i> &lt; 0.001). At 12 months, a higher body mass index (BMI) was associated with elevated T2*_s (<i>p</i> = 0.005), while semitendinosus-gracilis (STG) grafts (<i>p</i> = 0.018) and remnant preservation (<i>p</i> = 0.004) were associated with lower T2*_s values.</p> Conclusion <p>UTE two-component analysis captures temporal changes in graft after ACL reconstruction, suggesting collagen regeneration. Higher BMI may hinder, while STG grafts and remnant preservation may promote ligamentization.</p> Relevance statement <p>UTE two-component analysis serves as an imaging biomarker for ACL graft ligamentization, with higher BMI being associated with impaired ligamentization, while the use of STG grafts and remnant preservation may be associated with more favorable graft maturation at 12 months as assessed by UTE two-component MRI. These findings may help tailor rehabilitation protocols and guide graft selection.</p> Trial registration <p>This study was prospectively registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) under the identification number UMIN000045710 in October 2021.</p> Key Points <p><UnorderedList Mark="Bullet"> <ItemContent> <p>Ultrashort echo time two-component analysis noninvasively evaluates ligamentization of reconstructed ACL.</p> </ItemContent> <ItemContent> <p>Graft short T2* significantly decreased between 6 and 12 months postoperatively.</p> </ItemContent> <ItemContent> <p>Body mass index, graft type, and remnant status may influence graft maturation at 12 months.</p> </ItemContent> </UnorderedList></p> Graphical Abstract <p></p>