To obtain the subject agent highly safe, having sterilizing abilities against various pathogenic bacteria such as methicillin resistant Staphylococcus aureus or the like at a low concentration and persistence in sterilizing abilities and useful as a sterilizing agent for medical facilities by bringing the subject agent to contain an extract of Eucalyptus plant leaves with a polar solvent and chitosan.

This natural substance-originated bactericide is brought to contain (A) a polar solvent extract obtained by extracting leaves of Eucalyptus plants with a polar organic solvent, preferably a lower alcohol, etc., such as ethanol or the like and (B) chitosan in 0.0001-10 wt.% in the sum amount of the ingredients A and B. The ingredient A is preferably a fraction obtained by removing fats with a nonpolar organic solvent such as n-hexane or the like or refined oil by a steam distillation from leaves of Eucalyptus plants and extracting the leaves by a polar organic solvent. The ingredient A preferably contains a compound of the formula. This agent is useful for preventing from pimples and dermatophytosis.