With the increasing production and application of carbon nanotubes (CNTs), the quantity of CNTs in aquatic sediments is likely to increase over time. These CNTs may alter the sediments' physicochemical properties and influence the transportation of coexisting contaminants because of the CNTs large specific surface area and high porosity. In this study, the influence of multi-walled CNTs (MWCNTs) on sediment pore surface properties, hydrophobicity and the sulfamethoxazole (SMX) adsorption behavior were investigated. Meanwhile, the role of the aging processes of MWCNTs was also explored as these processes may alter the effects of MWCNTs on sediment properties. The results showed that the average pore size, external surface area (S-ext), total surface area (S-BET), and hydrophobic property clearly increased because of the MWCNTs contamination which enhanced the SMX adsorption capacity. Meanwhile, the pi-pi electron coupling/stacking between SMX and graphene surface of MWCNTs may be another factor increasing the SMX adsorption capacity. MWCNTs filling the sediment micro-pores decreased the isotherm linearity parameter (n) indicating an increase in adsorption intensity and heterogeneity. It was also found that the effects of MWCNTs on sediment pore surface properties and SMX adsorption significantly reduced during the aging processes from 0 to 2 months and subsequently leveled off, while, the aging processes had no effects on the hydrophobic property of the contaminated sediments. Aging mechanisms of MWCNTs in sediments may be mainly the pore blockage, surface coverage, and competitive adsorption of the nature organic matter (NOM) transferred from the sediments. These results may contribute to modelling and predicting the potential environmental risk of MWCNTs in natural aquatic sediments, particularly considering the influence of the aging process. (C) 2016 Elsevier B.V. All rights reserved.