Abstract: The degradation efficiency of organic pollutant by microorganisms is significantly modulated by soil type. Inorganic colloid is the fundamental matrix of soil and plays a critical role in governing the migrations and fates of environmental pollutants. This study aimed to clarify the roles of different soil inorganic colloids in the microbial degradation of organic pollutants, and four typical soils (Ultisol, Cambisol, Mollisol, and Anthrosol) were selected to extract inorganic colloids and to investigate their influences on the degradation of benzoapyrene (BaP) using Paracoccus aminovorans. The properties of these colloids were correlated with their performance in biodegradation experiments. The results demonstrate that inorganic colloids from all four soil types inhibited BaP degradation, with the inhibitory intensity following the order: Ultisol > Cambisol > Mollisol > Anthrosol. Comprehensive analyses using electron paramagnetic resonance (EPR), scanning electron microscopy (SEM), mineral composition determination, and bioavailability reveal that this inhibition primarily stems from two mechanisms: (1) the reduction of BaP bioavailability by the colloid, and (2) the impairment of Paracoccus aminovorans cell viability by persistent free radical mediated by iron oxide. Furthermore, the varying contents of kaolinite and montmorillonite in the different colloids were found to govern the BaP degradation efficiency. This work clarifies the key mechanistic roles of soil inorganic colloids in the microbial degradation of polycyclic aromatic hydrocarbons (PAHs), demonstrating their dual impacts on both pollutant bioavailability and microbial activity. These insights provide a critical theoretical foundation and a practical framework for designing effective microbial remediation strategies for PAH-contaminated soil.