The perceived impact of soil microplastics on soil aggregation is primarily attributed to their potential toxicity toward soil microorganisms. However, only a limited number of studies have undertaken comprehensive controlled experiments involving sterilized soils to substantiate this notion. The present study embarked on soil incubation experiments encompassing both non-sterilized soils and soils subjected to oven-heating sterilization to investigate the ramifications of polyethylene (PE) and polypropylene (PP) microplastics, characterized by mesh sizes of 30, 150, and 1000, on both the water-stability and mechanical stability of soil aggregates. The presence of microplastics decreased aggregation stability in Tianjin soils (on average -48.89% and -81.61% for 0.5-1 and 1-2 mm aggregates, respectively). The impact of microplastics was notably more evident in the non-sterilized soils. Microplastics also demonstrated the capacity to modify aggregate properties such as surface roughness. This study indicates the pivotal role played by interactions between soil microplastics and microorganisms on soil aggregation, but microplastics hold the potential to influence soil aggregation through non-biogenic pathways.