Salicylate is well-known to produce a reversible hearing loss and tinnitus. However, the mechanism of salicylate ototoxicity remain unresolved yet. Previous studies suggested that the increase of unknown compound concentration in perilymph of guinea pig might be important for the mechanism of salicylate ototoxicity. So we tried to compare the effect of unknown compound with that of sodium salicylate on eletrocochleographic changes. Using guinea pigs as experimental animals, sodium salicylate(460mg/kg) was injected untraperitoneally and unknown compound(5μl) was applied on round window membrane. Threshold of compound action potential(CAP) was determined at different time intervals. The loss of 30dBHL maximum CAP threshold was observed in 4 hours after intraperitoneal injection of sodium salicylate and the hearing was recovered to normal threshold in 24 hours. In another exprimental group, maximum CAP threshold loss was 21dBHL at 6 hours after applying of unknown compound on the round window membrane and the hearing was partially recovered in 24 hours. In the control groups, hearing threshold was changed within 6-7dBHL. This results suggested that unknown compound might be an important component inducing salicylate ototoxicity.