The antimicrobial activity of undecan-3-one, undecan-3-ol and its acetate was studied with respect to bacteria Escherichia coli and Bacillus subtilis, yeast Candida mycoderma and mould Aspergillus niger. The viability of the populations of the microbial strains tested in the presence of the studied compounds was assessed with the impedimetric method. It was found that the ketone did not cause a total inhibition of the growth of the studied bacteria populations, but it effectively affected the fungi. Alcohol obtained as a result of undecan-3-one reduction revealed better bacteriostatic activity while it was not active with respect to C. mycoderma. Undecan-3-ol ester was characterized by the poorest antimicrobial activity.