The microbicidal activity of a complex glutaraldehyde disinfectant was observed. The result showed that when the temperature of the test was 20 degrees C and 10% calf serum were added to the bacterial suspensions 2% diluted solution of the disinfectant for a two-minute contact could kill 99.99% of Staphylococcus aureus, and 1% diluted solution for two minutes could kill 99.99% of E. coli. The undiluted disinfectant with five-minute contact time could destroy the antigenicity of HBsAg. The undiluted disinfectant with thirty-five minute contact and 50% diluted solution with forty-five minute contact time could completely kill the spores of Bacillus subtilis var. niger under 50 degrees C. It was discovered that the germicidal concentration of the disinfectant was four times as high as the inhibition concentration and the used concentration determinal with capacity test was four times higher than as germicidal concentration when the three concentrations were compared. This result indicated that selection of suitable inactivator was very important. The practical concentration of disinfectant should be decided under the basis of the result from capacity test.