Abstract: Background The introduction of broad-leaved species into coniferous plantations is a practical approach for restoring soil structure. However, how this broad-leaved transformation regulates cementing agents to enhance soil aggregate stability remains unclear. Methods This study investigated pure Pinus massoniana plantations. (PM) and their mixed forests with Bretschneidera sinensis (PM×BS), Cercidiphyllum japonicum (PM×CJ), and Michelia maudiae (PM×MM). The effects of broad-leaved transformation on soil aggregate stability and cementing agents were examined. The cementing agents included soil aggregate organic carbon (SAOC) and iron/aluminum oxides in free (Fed/Ald), amorphous (Feo/Alo), and complexed (Fep/Alp) forms. Results 1) In the 0-20 cm soil layer, the content of >1 mm aggregates in PM×CJ and PM×MM increased by 8.76%-112.58% compared to PM, with significant increases in MWD, GMD, and R0.25. In the 20-40 cm soil layer, mixed forests significantly increased the content of >1 mm aggregates, and PM×CJ showed significant improvements in MWD, GMD, and R0.25 compared to PM. 2) Coniferous-broadleaf mixed forests significantly increased the SAOC content across all particle sizes in the 0-20 cm soil layer (with PM×MM exhibiting the highest values). Among all forest types, the content of iron and aluminum oxides was highest for Fed and Ald. Only in PM×BS, the Fed content in all aggregate sizes within the 0-40 cm layer was lower than in PM. 3) In the 0-20 cm soil layer, Fed, SOC, and Feo showed highly significant positive correlations with >1 mm aggregates (P < 0.01), with Fed contributing the most significantly to the positive enhancement of MWD. In the 20-40 cm soil layer, Ald played a dominant role in enhancing aggregate stability and exhibited a highly significant positive correlation with 1-0.5 mm aggregates (P < 0.01). 4) The contents of Fed, Feo, Ald, and SOC were significantly regulated by pH, showing significant (P < 0.05) or highly significant (P < 0.01) negative correlations. Conclusion The broadleaf transformation primarily enhances the stability of soil aggregates by increasing the contents of various forms of Fe/Al oxides in the soil. The research findings provide data support for soil restoration and sustainable management of P. massoniana plantations.