Multiple nanoparticles (NPs) have been released into the environment due to their increasing widespread applications. Studies have shown that the interactions between different types of NPs could have an impact on the adsorption of pollutants thereon. However, whether this impact depends on the particle size is still unknown. In this study, we have investigated the adsorption of sulfamethoxazole (SMX) on multi-walled carbon nanotubes (CNTs) in the presence of SiO2 (15, 30, and 100 nm) or Al2O3 (20, 50, and 100 nm). The results showed that SiO2 or Al2O3 inhibited the SMX adsorption by CNTs. Moreover, the inhibitory effects depended on both the particle size and the type of NPs. The inhibitory effect increased with increasing particle sizes of SiO2, but decreased with increasing particle sizes of Al2O3 due to their different heteroaggregation structures with CNTs. As demonstrated by DLVO theory calculations and TEM images, CNTs were prone to homoaggregate and then heteroaggregate with SiO2 in heterogeneous systems, and more CNTs were homoaggregated due to their stronger repulsion with larger SiO2 particles. This led to a greater inhibitory effect by larger SiO2 particles. In contrast, CNTs and Al2O3 tended to heteroaggregate rather than homoaggregate due to their oppositely charged surfaces. Fewer adsorption sites on the surface of CNTs were blocked by larger Al2O3 particles, which resulted in a decreased inhibitory effect of Al2O3 on SMX adsorption by CNTs with increasing particle sizes. This study highlights that the particle sizes of minerals will influence their effects on the adsorption of pollutants on CNTs in natural waters. (C) 2017 Elsevier B.V. All rights reserved.