Abstract: As a substitute for non-degradable plastics, biodegradable plastics are widely used in different fields. Compared with non-degradable plastics, biodegradable plastics will produce large amounts of microplastics in a short period of time in the environment. In order to explore the aging processes of the biodegradable plastics and their interactions with coexisting pollutants, the adsorption and desorption behaviors of sulfamethoxazole (SMZ) and amoxicillin (AMX) on the original and aged polylactic acid (PLA) were investigated, and polyethylene (PE) was studied for comparison. The results showed that: (1) The original PLA and PE had the characteristics of smooth surface and hydrophobicity. After heat-activated potassium persulfate aging, the particle size of PLA and PE decreased, plenty of pits, cracks and pores were produced on the microplastics surface, the specific surface area, the oxygen-containing functional groups, and the hydrophilicity increased. (2) The adsorption of antibiotics on PLA and PE conformed to the Pseudo-second-order model, and the main adsorption modes of original and aged PLA and PE were surface adsorption and intra-particle diffusion. (3) The adsorption capacity of PLA and PE increased after aging. The maximum adsorption capacity of SMZ by aged PLA was 14.7 mg/g, which was about 9.02 times that of original PLA (1.63 mg/g). The maximum adsorption capacity of SMZ by aged PE was 5.20 mg/g, which was about 3.01 times that of the original PE (1.73 mg/g). And the maximum adsorption capacity of aged PLA for antibiotics were greater than that of PE. (4) The desorption amount and desorption rate of the antibiotics of the aged PLA and PE decreased, but the desorption amount and desorption rate of the original and aged PLA were higher than that of PE. The results indicate that PLA has a stronger carrier effect for coexisting pollutants than PE. PLA releases antibiotics more easily than PE in organisms, which may pose a greater threat to the life and health of organisms.