Selection of antimicrobials to treat Asymptomatic bacteriuria (ASB) must be made with special considerations given to maternal and fetal toxicity. The study was conducted to check the effect of antimicrobial therapy for ASB in pregnant women and its effect on pregnancy outcome in Nair Hospital, Mumbai. The study included 3000 pregnant and 300 non–pregnant women. Microscopic examination of urine, identification of isolates and antibiotic sensitivity testing of isolates were carried out by standard methods.  Pregnant women screened were highest in second trimester (49.53%) and risk of ASB was highest in third trimester (8.7%). E. coli was leading bacteria isolated from 42.86.30% samples. Normal full term delivery was observed in 95.65% cases taking proper treatment for ASB. ASB in pregnancy leads to adverse effect on fetus and mother if not treated and which can be prevented by efficient screening and treatment.