The rapid growth of nanotechnology is stimulating research concerning the potential environmental impacts of manufactured nanomaterials. The present study summarizes, to our knowledge, the first examination regarding the potential effects of chronic exposure (32 d) of aquatic organisms (juvenile carp [Carassius auratus]) to sublethal concentrations (0.04–1.0 mg/L) of fullerene aggregates (nC60/aq; i.e., C60 suspended in water after long-term stirring) with average diameters of approximately 349 and/or 1,394 nm. The results demonstrated that the antioxidant enzymes superoxide dismutase and catalase were induced significantly in the gills and liver of C. auratus exposed to nC60/aq for 32 d, whereas a nonenzymatic antioxidant, glutathione, decreased in all tested tissues. In addition, lipid peroxidation (LPO) levels decreased in most cases, especially in the gills and brain, but exposure to 1.0 mg/L of nC60/aq led to a significant (p < 0.01) increase in the LPO level in the liver. This increase in LPO level in combination with the observed oxidative stress suggested that the liver might be the target of or most susceptible organ to nC60/ aq exposure. Furthermore, the body weight and total length of juvenile carp exposed to 1.0 mg/L of nC60/aq for 32 d decreased significantly (p < 0.05), indicating that nC60 /aq had an inhibitory effect on fish growth. The present findings imply that the oxidative stress induced by long-term exposure could be the main mechanism of the toxicity of nC60/aq to juvenile carp. This important work contributes to a better understanding of the potential health effects of exposure to manufactured nanomaterials on species in aquatic ecosystems.