Antimicrobial activity of thio-, thioxo- and oxo- derivatives of acridine has been studied. It was shown, that the majority of compounds possesses the moderate antimicrobial activity. It was established, that acetic acid (6-nitroacridinil-9-thio), piperidine salt (2-ethoxi-6-nitroacridinil-9-thio) and ethyl ether (acridinil-9-thio) of acetic acid show the expressed anti-bacterial activity with respect to gram-positive bacteria. The ethyl ether (acridinil-9-thio) of acetic acid also actively suppresses the growth of similar yeast fungus.