The high surface area of multi-walled carbon nanotubes (MWCNTs) tends to adsorb a large variety of toxic chemicals, which may enhance the toxicity of both MWCNTs and chemicals to organisms. In order to evaluate the combined toxicity of nonylphenol (NP) and MWCNTs to the earthworm Eisenia fetida in soil, artificial soil systems containing distilled water, 0.1 g kg(-1) MWCNTs, 1 g kg(-1) MWCNTs, 1 g kg(-1) MWCNTs absorbed 5 mg kg(-1) NP, and 10 mg kg(-1) NP alone were prepared and exposed to earthworms for 7 days. Antioxidative responses, and activities of cellulase, Na(+), K(+)-ATPase and acetylcholinesterase (TChE) as well as DNA damage were chosen as toxicological endpoints. The results showed that 1 g kg(-1) MWCNTs adsorbed 5 mg kg(-1) NP from the soil which caused much more adverse effects on the earthworms than each chemical alone, evident from the responses of cellulase, Na(+), K(+)-ATPase and comet assay. This study indicated that MWCNTs facilitated the bioavailability of NP to the earthworm and increased the harmful effects of NP.