To evaluate the toxicity of the ionic liquid 1-methyl-3-octylimidazolium bromide ([C 8 mim]Br) to Eisenia foetida, effects of [C 8 mim]Br on the growth, reproductive ability, and adenosine triphosphatase (ATPase) activity of earthworms were determined under laboratory conditions using artificial soil as substrate. The results showed that [C 8 mim]Br in high concentrations significantly inhibited the growth of the earthworms. These effects were enhanced with prolonged exposure to and increasing concentration of [C 8 mim]Br. E. foetida’s reproductive ability was significantly inhibited after 42d of subchronic exposure to [C 8 mim]Br at a concentration ≥5mgkg −1 artificial soil (dry weight). During acute exposure, a high concentration of [C 8 mim]Br ≥40mgkg −1 artificial soil (dry weight) inhibited the activities of Na + –K + –ATPase and Mg ++ –ATPase after 3 and 7d of exposure. After 42d of subchronic exposure, the activity of both ATPases was inhibited in groups exposed to ≥5mg[C 8 mim]Brkg −1 artificial soil (dry weight). These results indicate that treatment with the ionic liquid [C 8 mim]Br affects the growth, reproductive ability, and ATPase activity of earthworms E. foetida.