We found that an impurity was formed in the 1% dibucaine injection solution following ordinal treatment using the high-pressure steam method. The impurity was isolated and characterized to be 2-hydroxy-N-[2-(diethylamino) ethy1-4-quinolinecarboxamine (debutyl-dibucaine)], which was caused from the thermal degradation of dibucaine brought about by the sterilization process. The degradation of dibucaine with dealkylation was found to be affected under the thermal treatment, time and temperature conditions. In addition, suitable sterilization conditions were established to maintain the purity of the 1% dibucaine injection solution at more than 99.5%.