Breastmilk contains a large number and diversity of Human Milk Oligosaccharide (HMO) structures. These can be grouped in 3 main categories: core structures (e.g. LNnT, LNT), fucosylated- (e.g. 2’FL, DiFL) and sialylated structures (e.g. 3’SL, 6’SL). Different HMOs were reported to promote growth of specific bifidobacteria, as well as production of health-related bacterial metabolites. This study examined the impact of HMO diversity on infant gut microbiota and its metabolites in ex vivo fermentation systems with infant stool samples.