Acute toxicity and oxidative stress caused by exposure of titanium dioxide nanoparticles ($TiO_2$-NPs) in juvenile common carp (Cyprinus carpio) were investigated. $TiO_2$-NPs solution was prepared using deionized water and dispersed by sonication. Juvenile carp were exposed to different concentrations (5, 10, 20, 40, and 80 mg/L) of $TiO_2$-NPs. $TiO_2$-NP characteristics (particle morphology, size distribution, and zeta-potential) were analyzed using transmission electron microscopy (TEM) and dynamic light scattering (DLS). Different tissue samples (skin, liver, brain, and gill) of fish were dissected, and the biochemical responses (catalase [CAT] and glutathione S-transferase [GST] activities) were measured. The results showed that acute exposure to $TiO_2$-NPs induced GST and CAT levels to vary in all observed organs. The effective concentration of $TiO_2$-NPs was 20 mg/L in the liver and brain and 40 mg/L in the gill. Histopathological changes were as follows: (1) skin: hypertrophy and increased number of mucous cells and thickening of the epidermal layer; (2) gill: hypertrophy of chloride cells, degeneration of mucous cells, and increased acidification of mucous cells; and (3) liver: hyperplasia and cytoplasm vacuolation of hepatic cells. No lethal effects were observed during the acute test. Our results show that there is a potential risk of $TiO_2$-NP exposure to aquatic organisms in the environment.