Abstract: In order to reveal the influence of in-situ leaching of rare earth yttrium ore on farmland soilenvironment,the acute toxic effects of rare earth yttrium and ammonium sulfate ( leaching agent) pollu-tion on earthworms were studied by natural soil method. The results showed that the toxicity of only rareearth yttrium or ammonium sulfate was low. The LC50 values of rare earth yttrium and ammonium sulfatein 14 days were 1 216.57 mg /kg and 4 293.53 mg /kg,respectively,for earthworms. When the concen-tration of ammonium sulfate was higher than 4 400 mg /kg,the toxicity of rare earth yttrium increasedsignificantly and had a synergistic effect. Earthworms at the bottom of the food chain accumulated rareearth yttrium and might cause the gradual enrichment along the food chain. Close-