[Objective] Soil aggregate size distribution evolves due to soil aggregation and breakdown processes that occur under natural and anthropogenic impact. A change in aggregate size distribution can alter soil pore structure, which might also influence soil water transportation, gas exchange and microbial activities. Thus, this may potentially affect soil organic carbon (SOC) mineralization. Therefore, this study aimed to investigate the effect of aggregate size distribution on soil pore structure and the SOC mineralization.[Method] Soil samples were collected from a long-term field experimental site with treatments receiving different amount of pig manure (No manure, CK; Low manure, LM; High manure, HM). The soil samples were passed through sieves with 5.0(S₅), 2.0(S₂), or 0.5 mm(S_0.5) openings to create different aggregate size distributions, with the maximum aggregate sizes corresponding to 5.0, 2.0 and 0.5 mm, respectively. The sieved aggregates were repacked into soil columns (diameter 2.9 cm, height 4 cm) with a bulk density of 1.3 g·cm^-3. Soil columns were incubated for 57 days and SOC mineralization was measured during this period. Also, the soil pore structure was quantified using X-ray micro-computed tomography (μ-CT) imaging.[Result] Sieving altered soil aggregate size distribution, which resulted in significantly different soil pore structure in the repacked columns. Compared to S₅ and S₂ treatments, the S_0.5 treatment significantly decreased the image-based porosity (>16 μm) by 83.0%~93.9% and pore connectivity by more than 95%. The differences in macroporosity and pore connectivity between S₅ and S₂ treatmentwere significant for the HM soil, but not for the CK and LM soil. Also, aggregate size distribution had a significant effect on SOC mineralization. The breakdown of aggregates increased SOC mineralization. The cumulative SOC mineralization amount of S_0.5 treatment was 64.2%~79.1% and 14.1%~19.3% higher than that of S₅ and S₂ treatments for the CK and HM soils, respectively. However, there was no significant difference in the cumulative SOC mineralization between the S_0.5 and S₅ treatment in the LM soil. The correlation analysis indicated that the cumulative SOC mineralization amount was negatively correlated with the porosity of 16~30 μm pores.[Conclusion] Sieving broke down large aggregates and decreased soil macroporosity in the repacked soil columns. The breakdown of soil aggregates promoted SOC mineralization partially due to the release of the protected SOC. The change of aggregate size distribution and the resulting alteration of pore structure also correlated with SOC mineralization. This study can serve as a reference for future research related to SOC mineralization and the effect of soil aggregation on this process.