question: This review presents up-to-date information on the effects of microbiota on the individual chemotherapy sensitivity in cancer treatment. Recent studies have shown that a fine balance between the intestinal microbiota and the immune system is crucial for maintaining an efficacy of cancer chemotherapy. A number of antitumor drugs have complex mechanisms of action involving not only direct effects but also the activity of the intestinal microbiota and the immune system. A unique combination of these factors contributes to the individual chemotherapy sensitivity.