Antibiotics and microplastics are emerging contaminants that can negatively affect aquatic ecosystems. This study investigated the adsorption of five antibiotics (sulfadiazine, amoxicillin, tetracycline, ciprofloxacin, and trimethoprim) on five types of microplastics (polyethylene, polystyrene, polypropylene, polyamide, and polyvinyl chloride) in freshwater and seawater systems. Scanning Electron Microscope (SEM) and X-ray diffractometer (XRD) analysis showed that microplastics have different surface characteristics and varying degrees of crystallinity. Adsorption isotherms revealed that polyamide (PA) had the strongest adsorption capacity for antibiotics, with distribution coefficients (Kd) ranging from 7.36 ± 0.257 to 756 ± 48.0 L kg⁻¹ in freshwater. This was attributed to its porous structure and hydrogen bonding. Lower adsorption capacities were observed for the other four microplastics. The adsorption amounts of the five antibiotics on PS, PE, PP, and PVC decreased in the order of CIP > AMX > TMP > SDZ > TC, with Kd positively correlated with octanol-water partition coefficients (log Kow). In seawater, adsorption capacity decreased significantly, and no adsorption was observed for CIP and AMX. The results indicate that polyamide particles can serve as a carrier for antibiotics in the aquatic environment. Microplastics have varying physicochemical properties, including specific surface area, crystallinity, and pore size distribution, which may dominate their antibiotic adsorption capacities. Experiments were conducted to describe the structures and properties of five MPs using SEM and XRD, and to evaluate the adsorption capacities of five commonly used antibiotics in freshwater and seawater systems. The study used batch adsorption experiments with five concentration gradients (0.5, 1, 5, 10, and 15 mg L⁻¹) at room temperature (25 °C). The adsorption models used were linear, Freundlich, and Langmuir. The results showed that PA had the highest adsorption capacity for antibiotics, and the adsorption of antibiotics on microplastics varied between freshwater and seawater systems.Antibiotics and microplastics are emerging contaminants that can negatively affect aquatic ecosystems. This study investigated the adsorption of five antibiotics (sulfadiazine, amoxicillin, tetracycline, ciprofloxacin, and trimethoprim) on five types of microplastics (polyethylene, polystyrene, polypropylene, polyamide, and polyvinyl chloride) in freshwater and seawater systems. Scanning Electron Microscope (SEM) and X-ray diffractometer (XRD) analysis showed that microplastics have different surface characteristics and varying degrees of crystallinity. Adsorption isotherms revealed that polyamide (PA) had the strongest adsorption capacity for antibiotics, with distribution coefficients (Kd) ranging from 7.36 ± 0.257 to 756 ± 48.0 L kg⁻¹ in freshwater. This was attributed to its porous structure and hydrogen bonding. Lower adsorption capacities were observed for the other four microplastics. The adsorption amounts of the five antibiotics on PS, PE, PP, and PVC decreased in the order of CIP > AMX > TMP > SDZ > TC, with Kd positively correlated with octanol-water partition coefficients (log Kow). In seawater, adsorption capacity decreased significantly, and no adsorption was observed for CIP and AMX. The results indicate that polyamide particles can serve as a carrier for antibiotics in the aquatic environment. Microplastics have varying physicochemical properties, including specific surface area, crystallinity, and pore size distribution, which may dominate their antibiotic adsorption capacities. Experiments were conducted to describe the structures and properties of five MPs using SEM and XRD, and to evaluate the adsorption capacities of five commonly used antibiotics in freshwater and seawater systems. The study used batch adsorption experiments with five concentration gradients (0.5, 1, 5, 10, and 15 mg L⁻¹) at room temperature (25 °C). The adsorption models used were linear, Freundlich, and Langmuir. The results showed that PA had the highest adsorption capacity for antibiotics, and the adsorption of antibiotics on microplastics varied between freshwater and seawater systems.