Abstract: Effects of single-walled carbon nanotubes (SWCNTs) on physiological and biochemistrical characteristics of zebrafish were studied, using a semi-static test system. The zebrafish were kept in 0, 0.1, 1 and 10 mg•L^-1 SWCNTs-1 suspensions, separately for exposion up to 28 days, and then contents of glutathione (GSH) and maleic dialdehyde (MDA), and activities of superoxide dismutase (SOD) and Na⁺-K⁺-ATPase in brain, gill and liver were measured. Furthermore, impacts of purity of SWCNTs and dispersant (sodium dodecyl sulfate, or SDS) on biological toxicity of SWCNTs were also investigated. Results show that neither the dispersion nor the purity of SWCNTs was the main factor influencing its toxicity in the experiment, and no notable effect of SWCNTs was found on the content of GSH and the activity of SOD, but SWCNTs was found to have caused obvious increase in Na⁺-K⁺-ATPase activity and dose-dependent decline of MDA content in liver, gill and brain. Obviously, SWCNTs have no other obvious toxicity than stimulating zebrafish to intensify elimination of oxygen free radicals.