methods: Antibiotics in early life disrupt microbiota and increase obesity risk, whereas dietary agents such as prebiotics may reduce obesity risk. We examined how antibiotics administered with/without prebiotic oligofructose, alter metabolic and microbial outcomes in pregnant rats and their offspring. results: Pregnant rats were randomized to: 1) Control [CTR], 2) Antibiotic [ABT], 3) Prebiotic [PRE], 4) Antibiotic+Prebiotic [ABT+PRE] during the 3rd week of pregnancy and lactation. Offspring were fed a high fat/high sucrose (HFS) diet from 9-17 weeks of age to unmask obesity risk. ABT dams had higher body weight, body fat and leptin during lactation than all other groups. Prebiotics attenuated these outcomes and increased cecal Bifidobacterium. ABT offspring had higher body weight, fat mass and liver triglycerides after HFS diet, with a stronger phenotype in males; prebiotics attenuated these. At weaning, male ABT offspring had lower Lactobacillus while PRE and ABT+PRE offspring had higher Bifidobacterium and Collinsella. Fecal microbiota transfer from adult offspring cecal matter could not reliably transfer the obese ABT phenotype. conclusions: Antibiotic use during pregnancy/lactation increases adiposity and impairs post-partum weight loss in dams. Co-administering prebiotics with antibiotics in rat dams prevented obesity risk in offspring and was associated with altered gut microbiota. This article is protected by copyright. All rights reserved.