Objective — to study the possibility of prophylactic use of probiotic Vagilac in sexually active girls with initial symptoms of vaginal disbiosis. Material and methods. 50 girls aged 14 to 17 years (16.2±0.1) were divided into three groups: group 1 (22 patients) — with the normal level of pH (4.0—4.4), group 2 (20) and 3 (8) — with abnormal high level of pH (4.5 to 5.0) and above 5.2 respectively. 2 new groups were allocated from girls of  groups 2 and 3 in which no STIs and urogenital infections have been identified: a group with bacterial vaginosis (BV) — 10 patients and a group with only increased pH level — group with vaginal disbiosis (DV) — 7 patients. Vagilac capsules 180 mg bd were prescribed to patients of BV and DV groups for 14 days with the following assessment of complaints and the dynamics of pH in 14 days after treatment. Results. A. vaginae was not found in group 1, but it was found in 6 (30.0%) patients of  group 2 (p<0.01; χ2= 5,44; p=0.020; TMF: p=0.007 ) and in 2 (25%) girls of group 3. C. trachomatis, M. hominis, M. genitalium, U. urealyticum were found only in patients of groups 2 and 3.  In 17 girls of groups 2 and 3 no  STIs and cervical leukocytosis have been identified. There were no differences in character of complaints and vaginal PH in groups BV and DV. After treatment with Vagilac 100% girls of DV group and only 60% of BV group (TMF: p=0.007) reported subjective improvement. pH level was decreased up to normal level in 60% of patients of  group BV, but in 40% was even increased. In DV group pH did not get back to normal level in one girl only. Conclusion. Oral administration of Vagilaс may be the first step in the treatment of sexually active teenagers with initial symptoms of vaginal disbiosis in order to prevent the development of more severe disbiotic disorders and acute inflammation of the uterus appendages.