Abstract: 8-Hydroxyquinoline-antimony complex synthesized in our Institute is a new antimonial com- pound for oral use.Its LD₅₀ for mice,was 7.3—11.4 mg/20g body weight while that of tartar emetic was 3.2—4.2 mg/20g body weight.Even with the same process of preparation different Sb contents of 21.0,23.1,25.5,43.2 and 51.3% have been obtained with differences in toxicity in increasing order.Within the limit of 21.0 to 25.5%,no difference in toxicity nor in efficacity was observed in treated animals.However,different methods of preparation resulted in significant difference in toxicity and efficacy even when the antimony contents were the same. When 8-hydroxyquinoline-antimony complex and tartar emetic were used at the total dosages of 1/2 or 1/3 LD₅₀×14 to treat experimentally infected mice per os in 7,10,14 and 20 day’s courses,the efficacity of 8-hydroxyquinoline-antimony complex was superior to,but the toxicity lower than,that of tartar emetic. Furthermore,it was found that under the dose-schedule used,pathological lesions caused by 8-hydroxyquinoline-antimony complex were similar to those caused by tartar emetic.They occur chiefly in the mucous membrane of the stomach and intestine,while the damage to the liver was rather slight.