Streptococcus agalactiae (Group B streptococcus, GBS), a member of normal fl ora of human gastrointestinal and genitourinary systems, is a leading cause of sepsis, meningitis, and pneumonia particularly in newborn. GBS can also cause severe infections in pregnant women and adults with underlying disease, as well as mild diseases, such as urinary tract infections (UTIs). GBS strains exhibit 10 different serotypes, and the identifi cation of serotype distribution is important epidemiologically. The role of biofi lm production is one of the virulence factors that has been discussed in the pathogenesis of GBS infections. Although resistance to penicillin and ampicillin has not been documented in GBS, different rates of resistance has been reported for the alternative antibiotics to penicillin. The aim of this study was to investigate the serotype distribution, the ability of biofi lm formation and the antibiotic susceptibilities of S.agalactiae strains isolated from urine cultures. A total of 60 strains were included in the study, 40 of them were isolated from patients (38 female 2 male; mean age: 36.7 years) with urinary tract complaints whose cultures yielded single type of colonies in the number of >= 50.000 cfu/ml, whereas 20 of them were isolated from patients (19 female 1 male; mean age: 37.2 years) without urinary tract complaints whose cultures yielded mixed colonies in the number of <= 20.000 cfu/ml. Chromogenic media were used for the isolation and the isolates were identifi ed by conventional methods. The isolates were then serotyped by latex agglutination method and their antibiotic susceptibilities were determined by disk diffusion method recommended by CLSI documents. Biofi lm formation of the strains were investigated by microplate and Congo red agar (CRA) methods. In our study, the most frequently detected serotypes were V (n= 18; 30%) and II (n= 14; 23.3%), followed by serotype Ia (n= 10; 16.7%), III (n= 9; 15%), Ib (n= 3; 5%), VI (n= 1; 1.7%) and VII (n= 1; 1.7%). Serotype IV, VIII and IX were not detected, while four (6.7%) isolates were untypeable. Serotype V (13/40; 32.5%) and serotip II (6/20; 30%) were in the fi rst line among the strains isolated from patient and control groups, respectively. All of the GBS isolates were found susceptible to penicillin, vancomycin and cefotaxime. The rates of resistance against ofl oxacin, erythromycin and clindamycin in patient group were found as 22.5%, %10 and 5%, respectively. In the control group resistance rates against erythromycin and clindamycin were both 10%, while no resistance was detected to the other antibiotics. The ofl oxacin resistance in the patient group was found signifi cantly higher than that of control group (p= 0.02). By microplate method, the percentage of moderate/strong biofi lm producers was found as 42.5% (17/40) in the patient group and 20% (4/20) in the control group, however the difference between the groups was not statistically signifi cant (p= 0.08). All GBS strains were detected as positive by the CRA method, and it has been suggested that this might have been due to the binding of Congo red to sialic acid found in the GBS capsule, therefore this method thought to be improper for the investigation of biofi lm formation in GBS strains. In conclusion, the most frequent serotypes of the GBS urinary isolates in our study were similar with the frequent serotypes reported in other studies. Our data have pointed out that the biofi lm formation of GBS may not play a role in the pathogenesis of UTIs. In the meantime the high quinolone resistance detected in our study should be considered in the treatment of UTI due to GBS.