[en] The influence of variation in carbohydrate (CHO) composition within the same type of cereal on intestinal fermentation patterns and microbial community composition in the pig is unknown. Ten hulless barleys (HLB), 6 hulled barleys (HB), 6 oats (O) and 6 oat groats (OG) were studied in vitro. These cultivars differed in β-glucan, non-starch polysaccharides (total, soluble and insoluble), starch content and structure. They were hydrolyzed enzymatically, inoculated with pig feces and fermented for 72h. Fermentation kinetics was modelled, and microbial composition and short-chain fatty acid (SCFA) profiles analyzed using TRFLP and gas chromatography. Multivariate analysis revealed that microbial profiles, SCFA and fermentation parameters were affected by CHO composition but differently according to the grain type (HLB, HB, O or OG). Members of Clostridium cluster XIVa were associated to higher amylose contents and butyrate production in HB cultivars and in HLB cultivars. Several clostridia phylotypes were positively influenced by β-glucan content in HLB and HB. Cellulolytic Ruminococcus-like bacteria were increased with cellulose content in HB, HLB and OG and these bacteria tended to increase acetate production in general. Bacteroides-like bacteria were positively affected by amylopectin and starch content of barley cultivars. Cereal cultivars differing in CHO composition can alter the pig intestinal microbial ecophysiology to possibly improve gut health.