Antibiotic therapy and long-term antibiotic prophylaxis affect the normal flora of the gastrointestinal tract in the patients with recurrent pyelonephritis. It may disturb the balance in oxalate-degrading bacteria in colon and induce hyperoxaluria. The aim of this study was to investigate the level of colon oxalate-degrading bacteria colonization inpatients with recurrentpyelonephritis and its association with administration ofantibiotics. Patients and methods. The pilot observational cross-sectional study, involving 12 patients with uncomplicated recurrent pyelonephritis, non-stone formers. Oxalate-degrading bacteria in feces were identified by bacteriological culture method in the sodium oxalate reach medium. Results. Oxalate-degrading bacteria were detected in feces of 6 (50%) surveyed patients. The number of oxalatedegrading bacteria ranged from 2,0 to 7,0 lg CFU/g in feces and depended on the time after the last administration of antibiotics (F = 4,6; P = 0.05). The levels of oxalate-degrading bacteria colonization and urinary oxalate excretion in surveyed women had a moderate inverse correlation (p =-0,6;P = 0.03). Conclusions. The significantly higher urinary oxalate excretion in women non stone-formers with recurrent pyelonephritis may be associated with the application of antibiotics and a subsequent decolonization of oxalate-degrading bfcteria:     must befurther confirmed in ranaomizea study.