INTRODUCTION: The beneficial effect of probiotics on the improvement of carbohydrate and lipid metabolism, as well as body mass index (BMI), has been demonstrated in various patient groups. We aimed to investigate the effect of a multi-strain probiotic on the hormonal balance of women with PCOS. Ethical approval was obtained from the Bioethical Committee. METHODS: The study was designed as a 12-week, randomized, double-blind, placebo-controlled clinical study. The probiotic SanProbi RESULTS: A comparison of changes in individual hormone levels between groups confirmed statistically significant differences for TSH, androstenedione, SHBG, and BMI. In the case of LH, the statistical significance of the difference in delta change in the probiotic group was demonstrated with the use of a one-tailed test. CONCLUSIONS: Probiotic supplementation may serve as an alternative supporting treatment, especially in the phenotype of women with a high FAI index. Probiotic therapy is also effective in reducing BMI in overweight women with PCOS.