Nanoplastics (NPs) and Microcystins (MCs) are widely distributed in the aquatic environment, and ultraviolet (UV)-aging can change the surface properties of NPs, thereby influence the adsorption behavior of NPs to the co-existing pollutants. In the present study, we investigated the influence of UV aging on the adsorption of MCs by polystyrene nanoplastics (PSNPs) and explored toxicity variations among pristine, aged, and MCs-loaded PSNPs to human HepG2 cells.