Abstract: This study investigated the effects of ultraviolet (UV) aging on the Cu(II) adsorption mechanisms onto non-biodegradable polyamide (PA) and biodegradable polylactic acid (PLA) microplastics, as well as the differences in pathogenic bacterial colonization on their surfaces. Simulated UV aging simulation experiments were performed. The physicochemical properties of the microplastics before and after aging, were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Adsorption kinetics and isotherm models were employed to elucidate the Cu(II) adsorption mechanisms. High-throughput 16S rRNA sequencing was utilized to examine changes in the surface microbial community structure and pathogenic colonization patterns. The results demonstrated that UV aging significantly increased the surface roughness of both types of microplastics. Notably, the maximum Cu(II) adsorption capacities of PA and PLA grew from 0.1022 mg/g and 0.9890 mg/g to 0.9605 mg/g and 2.457 mg/g, respectively. The adsorption behavior followed the pseudo-second-order kinetic model and the Langmuir isotherm. After Cu(II) adsorption, the abundance of pathogenic bacteria increased on both microplastics, with PA exhibiting higher pathogenic abundance and diversity than PLA. Overall, UV aging promoted Cu(II) adsorption by altering the surface properties of the microplastics. Given its long-term association with a greater abundance of pathogens, non-biodegradable PA may pose a higher environmental risk.