Introduction: Preterm birth is the leading cause of perinatal morbidity and mortality. Bacterial vaginosis is a condition characterized by an alteration of the vaginal ecology in which the normal flora, dominated by lactobacilli, is replaced by a mixed bacterial flora which includes Gardnerella vaginalis, Mobiluncus species, Mycoplasma hominis. The prevalence of bacterial vaginosis among pregnant women varies from 6-32% in various studies. The classic symptoms of bacterial vaginosis include vaginal discharge and fishy odour. Its Complications of Bacterial vaginosis include spontaneous abortion, preterm labour and delivery, premature rupture of membranes. Aim of study: To assess the role of bacterial vaginosis in Preterm labour. Materials and methods: Prospective case control study done in all Antenatal cases with gestational age 28 weeks to 37 weeks attending the OPD or admitted in the department of OBG at Sri Siddartha Medical College, Tumakuru for duration of 24 months. Results: The incidence of Bacterial vaginosis in preterm labour cases was 31.2%. The mean gestational age who has gone into preterm labour was 32-36 weeks. Amsel’s criteria and Nugent score on examination, was statistically significant on comparison of cases and controls (p=0.0006). Conclusion: Bacterial vaginosis in pregnancy is associated with adverse pregnancy outcomes including preterm labour, low birth weight and puerperal sepsis. Thus screening for bacterial vaginosis in all pregnant women complaining of vaginal discharge is essential