Acepromazine maleate(sedaject) was injected to 3 and 5 thoroughbred racehorses at 0.2mg/kg/bw, intramurculary(IM) and 0.1mg/kg/bw, intravenously(IV) respectively, and investigated the changes of clinical signs and blood pictures In before and after injection. Sedation was induced within 15 minutes after injection at the two groups and general sedation with towering of the upper eyelids and penile protrusion lasted about 7~9 hours and 9~11 hours at IV group and IM group following injection respectively. Heart beat and respiratory rates were induced within 15 minutes and then slowly returned to preinjection levels at 3 and 7 hours in the two group following injection respectively. Body temperature was decreased within IS minutes and the effect was Peaked after 30 minutes and 3 hours in IV group and IM group respectively, and then slowly returned to preinjection levels. RBC parameters, Hb and PCV were decreased about 30% at 1~5 hours and then returned to preinjection values at 13~24 hours in two groups Total WBC number were decreased slightly within 30 minutes and then returned to preinjection level at 13~24 hours in IV group but being still decreased 24 hours after dosing in IM group serum glucose level, SGOT and ALP activity were not changed significantly. Generally the set of sedation and awakening signs were faster in IV group than in IM group and RBC parameters and total WBC were depressed markedly in IM group than in IV group.