In the present study, goldfish toxicity and superficial damage from 1-methyl-3-octylimidazolium bromide ([C8mim]Br) exposure were evaluated by an acute toxicity test. These results show that the 24-h 50% lethal concentration for [C8mim]Br in goldfish is 244 mg L−1, and this indicates that [C8mim]Br is a chemical with moderate or low toxicity to organisms. Scanning electronic microscope and histological observations revealed that acute exposure to [C8mim]Br induced obvious superficial damage to the skin, gill filaments, and intestinal villi of the goldfish, and this suggests that the skin, gills, and intestines may be the first direct targets of the ionic liquid in this fish. Histological examination also indicated that [C8mim]Br-exposure caused damage to the goldfish's hepatopancreas and kidney, consisting mainly of hepatic cords in a loose connection, hepatic cytoplasmic vacuolation, renal parenchyma vacuolization, and intumescence of the renal tubule. In addition, we found that [C8mim]Br caused a significant increase in malondialdehyde (MDA) level in the hepatopancreases from these goldfish, and thus we suggest that the MDA level may be a biomarker of [C8mim]Br-toxicity in goldfish. © 2011 Wiley Periodicals, Inc. Environ Toxicol, 2013.